Three dimensional integrated circuit

ABSTRACT

Implanting ions to form a cleave layer in a semiconductor device causes damage to sensitive materials such as high-K dielectrics. In a process for forming a cleave layer and repairing damage caused by ion implantation, ions are implanted through a circuit layer of a substrate to form a cleave plane. The substrate is exposed to a hydrogen gas mixture for a first time at a first temperature to repair damage caused by the implanted ions. A cleaving process may then be performed, and the cleaved substrate may be stacked in a 3DIC structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of U.S. application Ser. No.15/899,622, filed Feb. 20, 2018, which claims priority to provisionalapplication No. 62/460,653, filed Feb. 17, 2017, and is a continuationin part of U.S. application Ser. No. 15/829,442, filed Dec. 1, 2017 (tobe issued as U.S. Pat. No. 10,049,915 on Aug. 14, 2018), which is acontinuation in part of U.S. application Ser. No. 15/618,048, filed Jun.8, 2017, which is a continuation of U.S. Pat. No. 9,704,835, issued onJul. 11, 2017, which claims priority to each of the followingprovisional applications: U.S. Provisional Patent Application No.62/120,265, filed Feb. 24, 2015, and U.S. Provisional Patent ApplicationNo. 62/101,954, filed Jan. 9, 2015. Each of these documents isincorporated in its entirety herein.

BACKGROUND

Semiconductor substrates in conventional chip stacks are typicallythinned using a mechanical backgrinding process. Backgrinding imparts ahigh level of mechanical stress to the devices and can result insubstantial thickness variation. Therefore, other processes forseparating substrates are desirable.

One approach to substrate thinning is described in U.S. Pat. No.6,316,333 (hereinafter, “Bruel”). Bruel describes implanting ionsthrough gate structures to form a cleaving plane in a substrate andremoving a portion of the substrate by cleaving along the cleave plane.Bruel acknowledges that ion implantation causes damage to devicestructures, e.g, channel regions, that can render the devicesinoperable. Bruel describes building structures on the exposed surfaceof a substrate to selectively block ion implantation, thereby reducingdamage to structures that are disposed directly beneath the blockingstructures.

However, there are several limitations to Bruel's proposal. Thestructures described by Bruel are relatively large, e.g. gate lengths of0.5 microns. Current devices use structures that are much smaller, e.g.gate lengths of 30 nanometers or less, which are more than an order ofmagnitude smaller than the gate length described by Bruel. In order toaccumulate sufficient hydrogen ions to perform a cleaving operation,ions must be implanted through a substantial portion of a devicesurface. Moreover, modern devices are increasingly complex and includehigher quantities of sensitive structures. Some of these structures,such as vertical transistors, have vertical components that are longerthan horizontal components, which presents a greater opportunity fordamage from a vertically oriented ion that passes through the structure.

In addition, larger structures are generally more robust to ion damagethan smaller structures. A smaller structure will have fewer atoms andbe more sensitive to the disruption of an atom within the structure. Forexample, a barrier layer that has a feature size of 10 nm may have athickness in the tens of atoms, so that disruption of a single atom mayhave a significant effect on the barrier property.

TECHNICAL FIELD

The present disclosure relates generally to the manufacture ofintegrated circuit devices. More particularly, the present disclosureprovides a method and resulting devices for stacking and interconnectingthree-dimensional devices using heterogeneous and non-uniform layers,such as fully fabricated integrated circuits. By way of example, theintegrated circuits can include, among others, memory devices, processordevices, digital signal processing devices, application specificdevices, controller devices, communication devices, and others.

SUMMARY

Embodiments of the present disclosure relate to semiconductor devicesincluding ion cleaving technology. Embodiments may be employed to formthree-dimensional integrated circuit (3DIC) by implanting ions through acircuit layer to form a cleave plane, repairing damage caused by theimplantation, and stacking semiconductor substrates. The substrates maybe processed at the wafer scale.

In an embodiment, process of forming a 3DIC includes providing a firstsubstrate with a circuit layer that includes plurality of dielectric andconductive structures, implanting ions through the circuit layer andinto the first substrate to form a cleave plane, and after implantingthe ions through the circuit layer, exposing the semiconductor substrateto a hydrogen gas mixture for a first time at a first temperature torepair damage caused by the implanted ions. A first portion of the firstsubstrate with the plurality of dielectric and conductive structuresdisposed thereon is separated from a second portion of the firstsubstrate by cleaving at the cleave plane, the first portion of thesubstrate is bonded to a second substrate. At least a portion of theconductive structures of the first substrate may subsequently beconnected to conductive structures of the second substrate. The firsttemperature may be from 300 C to 500 C, and the time may be at leastone-half hour. The conductive and dielectric structures may includehigh-K dielectric structures comprising at least one material with a Kof 10 or greater.

The first and second substrates may be wafer scale substrates, and thefirst substrate may not be exposed temperatures above, for example, 300C, 400 C, 450 C or 500 C after implanting the ions and before separatingthe first portion from the second portion.

In an embodiment, the hydrogen gas mixture has at least 1% hydrogen gasand a remainder of the gas mixture is one or more inert gas. Forexample, the gas mixture may be a forming gas.

The ions may be implanted at a temperature of less than 100 C and aproton energy that is sufficient to place a majority of recoil damageand the cleave plane deeper than a depletion layer thickness of anoperating transistor.

In an embodiment, a process for repairing damage caused by implantingions through a circuit layer that includes conductive and dielectricstructures into a semiconductor substrate is performed by exposing thesemiconductor substrate to a hydrogen gas mixture for a first time at afirst temperature after implanting ions through the conductive anddielectric structures of the semiconductor substrate. The conductive anddielectric structures may include high-K dielectric structures thatinclude at least one of hafnium oxide (HfO₂), hafnium silicon oxide(HfSiO₂), hafnium silicate (HfSiO₄), tantalum oxide (TaO₅), tungstenoxide (WO₃), cerium oxide (CeO₂), titanium oxide (TiO₂), yttrium oxide(Y2O₃), strontium titanate (SrTiO₃), lanthanum aluminate (LaAlO₃),niobium pentoxide (NiO₅), zirconium silicate (ZrSiO₄) and zirconiumoxide (ZrO₂).

The hydrogen gas mixture may have at least 1% hydrogen gas and aremainder of one or more inert gas, such as a forming gas. The exposuretime may be at least 30 minutes, and the first temperature may be, forexample, from 300 C to 500 C or from 350 C to 450 C. In an embodiment,the first time is from one half hour to five hours and the firsttemperature is from 350 C to 450 C.

In an embodiment, the dielectric structures may include at least onedielectric material with a K of 20 or more, the first temperature isfrom 300 C to 500 C, the hydrogen gas mixture includes at least 1%hydrogen, and the temperature is at least 30 minutes, and the ions areimplanted to form a cleave plane below the circuit layer.

A method of forming a device includes providing a first substrate,depositing a thickness of range compensating material on a first surfaceof the first substrate, implanting ions into the first substrate, theions traveling through the range compensating material to define acleave profile in the first substrate, the cleave profile including atleast one contour that corresponds to the thickness of absorbermaterial, removing the absorber material, and cleaving the firstsubstrate at the cleave profile, thereby exposing the at least onecontour. In an embodiment, the at least one contour is a coolantchannel. The range compensating material may be a photoresist material.

The method of forming a device may include, after cleaving the firstsubstrate, coating exposed surfaces of the coolant channel with acoating layer. The coating material may be a material that prevents achemical reaction between a coolant fluid and the first substratematerial. For example, the coating material may be a nitride material oran oxide material. The thermal conductivity of the coating material maybe higher than a thermal conductivity of a bulk material of the firstsubstrate. In some embodiments, the first substrate has a thermalconductivity that is greater than 130 W/m-K at a temperature of 25degrees Celsius. The first substrate may include carbon, for example inembodiments in which the first substrate is a diamond or graphitematerial.

After cleaving, the cleaved surface of the first substrate may be bondedto a second substrate having a circuit layer. In such an embodiment, thebond may be formed by an oxide layer deposited on a surface of thesecond substrate. When the range compensating layer is removed, a bondlayer may be deposited on the first surface of the first substrate, andused to bond a third substrate comprising a circuit layer to the bondinglayer on the first surface of the first substrate. The first, second andthird substrates may be wafer scale substrates.

In some embodiments, hydrogen ions are implanted through one or morecircuit layer that includes high-K dielectric and conductive elements.In such embodiments, ion implantation may damage the dielectric andconductive elements. The damage may be repaired by exposing thesubstrate to an atmosphere that includes a hydrogen gas and an inert gasat a temperature of from 350 degrees Celsius to 500 degrees Celsius forat least 30 minutes to repair damage to the dielectric structures.

In an embodiment, a method for forming a stacked semiconductor deviceincludes implanting ions through dielectric and conductive structures ofa first substrate to define a cleave plane in the first substrate,cleaving the first substrate at the cleave plane to obtain a cleavedlayer including the dielectric and conductive structures, bonding atleast one die to the first substrate, the at least one die having asmaller width than a width of the first substrate, depositing aplanarization material over the at least one die, planarizing theplanarization material to form a planarized upper surface over the atleast one die, and stacking a third substrate on the planarized uppersurface.

The ions may be implanted at a temperature of 100 degrees Celsius orless. In an embodiment the ions are implanted at room temperature.

In some embodiments, a total thickness variation (TTV) of materialcleaved from the substrate is 4% or less, 2% or less, or 1% or less. Thefirst, second and third substrates may be wafer scale substrates.Furthermore, after cleaving the first substrate, the first substrate maybe annealed to repair damage to the dielectric and conductive structurescaused by the ions.

In an embodiment, an annealing process that repairs damage to thedielectric and conductive structures is performed at a temperature of350 Celsius or greater in an environment that includes hydrogen gas.Conditions in a repair process should be sufficient to allow hydrogen topenetrate the device surface and bond to a molecule that was damaged byan implantation process. In one specific embodiment, the repairannealing is conducted at a temperature of 400 Celsius in an atmospherethat includes from 2 to 5 percent hydrogen, with a remainder being oneor more inert gas. In an embodiment, the repair annealing is conductedfor a period of time that is sufficient to allow the hydrogen gas todiffuse though circuit structures in a device, which may include aninterconnect network of metal and low-dielectric constant dielectricmaterial, and to occupy passivating sites at damaged dielectric bonds.In an embodiment, annealing is conducted at a temperature of 400 Celsiusfor one hour.

An embodiment may include depositing a dielectric material over the atleast one die after bonding the at least one die to the first substrateand before bonding the third substrate over the at least one die.

Before implanting the ions, a range compensating layer may be formedover the first substrate.

After the first substrate is cleaved, the first substrate may be bondedto a second substrate. In an embodiment, the second substrate has seconddielectric and conductive structures, and the second substrate is formedby implanting ions through the second dielectric and conductivestructures. The first, second and third substrates may be wafers.

A small die may be one of several types of devices, including anamplifier, a RF tuner, a radio tuner, a Light Emitting Diode, and anoptical sensor.

The plurality of conductive structures bay be a plurality of transistorswith a respective plurality of conductive gates that are separated fromrespective channel regions by gate dielectrics.

In an embodiment, a method of forming a three-dimensional integratedcircuit includes providing a first semiconductor substrate with a firstcircuit layer including conductive metal and dielectric materials,implanting ions through the plurality of conductive metal and dielectricmaterials of the first circuit layer to create a first cleave plane inthe first substrate, cleaving the first substrate at the first cleaveplane, providing a second semiconductor substrate with a second circuitlayer including conductive metal and dielectric materials, implantingions through the conductive metal and dielectric materials of the secondcircuit layer to create a second cleave plane in the second substrate,cleaving the second substrate at the second cleave plane, bonding thefirst substrate to the second substrate, stacking at least one die onthe second substrate, the die having a width that is less than a widthof the first plurality of circuit structures, depositing a planarizationmaterial over the at least one die, planarizing the planarizationmaterial to form a planarized upper surface over the at least one die,and stacking a third substrate on the planarized upper surface.

In an embodiment, a method of forming a semiconductor device includesforming an ion range compensating layer over a surface of a firstsubstrate, implanting ions through the ion range compensating layer anddielectric and conductive structures of the first substrate to define acleave plane in the first substrate, cleaving the first substrate at thecleave plane to obtain a cleaved layer including the dielectric andconductive structures, bonding at least one die to the first substrate,the at least one die having a smaller width than a width of the firstsubstrate; depositing a planarization material over the at least onedie, planarizing the planarization material to form a planarized uppersurface over the at least one die, and stacking a third substrate on theplanarized upper surface.

According to the present disclosure, techniques generally related to themanufacture of integrated circuit devices are provided. Moreparticularly, the present disclosure provides a method and resultingdevices for stacking and interconnecting three-dimensional (3-D) devicesusing heterogeneous and non-uniform layers, such as fully fabricatedintegrated circuits. By way of example, the integrated circuits caninclude, among others, memory devices, processor devices, applicationspecific devices, controller devices, communication devices, and others.

A method comprises providing a first substrate having dielectricstructures and conductive structures. Ions are implanted into the firstsubstrate, the ions traveling through the dielectric structures and theconductive structures to define a cleave plane in the first substrate.The first substrate is cleaved at the cleave plane to obtain a cleavedlayer having the dielectric structure and the conductive structures. Thecleaved layer is used to form a three-dimensional integrated circuitdevice having a plurality of stacked integrated circuit (IC) layers, thecleaved layer being one of the stacked IC layers.

Three-dimensional stacking and interconnection of heterogeneous andnon-uniform layers, such as fully fabricated integrated circuits areprovided. Techniques are included for a substantial reduction ininter-layer separation and increase in the available inter-layerconnection density, leading to increased signal bandwidth and systemfunctionality, compared to existing chip stacking methods usinginterposers and through-Silicon vias (TSVs). The present techniquesextend the use of high-energy proton implants for splitting and layertransfer developed for homogeneous materials, such as the fabrication ofSilicon-on-Insulator (SOI) wafers, with modifications appropriate forlayer transfer of heterogeneous layers and consideration for damageeffects in device structures.

In an example, the present disclosure provides techniques including amethod for fabricating an integrated circuit. The method includesproviding a semiconductor substrate comprising a surface region, aplurality of transistor devices formed overlying the surface region, aninterlayer interconnect region comprising a structured metal layer and astructured dielectric layer and an inter-layer connection overlying theplurality of transistor devices, and a dielectric material overlying theinterconnection region to provide a bonding interface, although therecan be variations. The method includes forming an unpatternedphotoresist material overlying the bonding interface provided from thedielectric material. In an example, the unpatterned photoresist materialis configured to shield one or more of the plurality of transistors fromelectromagnetic radiation in a wavelength range of below 400 nm and toselectively adjust a depth of a subsequent implanting process. Themethod subjects the unpatterned photoresist material to the implantationprocess to introduce a plurality of hydrogen particles through theunpatterned photoresist material to a selected depth to a cleave regionunderlying the surface region of the semiconductor substrate to define atransfer device between the cleave region and a surface of thedielectric material to form a thickness of a multi-layer of a pluralityof interconnected conductive metal layers and insulating dielectrichaving a total metal thickness of 3 to 5 microns or less. The methodremoves the unpatterned photoresist material after the hydrogen implantstep. The method bonds the surface of the dielectric material overlyingthe transfer device to a transfer substrate to temporarily bond thesemiconductor substrate to the transfer substrate.

In an example, the method subjects sufficient energy to a portion of thecleave region to remove an upper portion of the semiconductor substratefrom a lower bulk substrate material, while using the transfer substrateto hold the upper portion of the semiconductor substrate such that theupper portion comprises a hydrogen damaged region. The energy can beprovided spatially or globally as described in U.S. Pat. No. 6,013,563(the '563 patent) assigned to Silicon Genesis Corporation, claimspriority to May 12, 1997, and lists Francois J. Henley and Dr. NathanCheung, as inventors, commonly assigned, and hereby incorporated byreference in its entirety. In an example, the method subjects thehydrogen damaged region overlying the transfer device to a smoothingprocess to remove a portion or all of the hydrogen damaged region and toform a backside surface. In an example, the method forms a thickness ofdielectric material overlying the backside surface.

In an example the backside surface is configured with one or moreprovisions for formation of an inter-layer conductive path linking to abottom landing pad in the structured metal layer of the transfer deviceand a landing pad for a bonded conductive path to an adjacent devicelayers.

In an example, the method further comprises depositing a dielectriclayer to form a suitable bonding interface on the structured metallayer, the structured metal layer comprising a 5 to 10 microns thickconducting layer formed over a densely patterned metal interconnectmulti-layers for provision of a device power signal, a ground signal anda frequency synchronization signal, and the dielectric layer having aplurality of conductive paths through the dielectric layer on forbonding with inter-layer conductors in an upper, transfer device layer.

In an example, the method further comprises aligning of the transferdevice layer to the semiconductor substrate to permanently bond theinter-layer conducting path. In an example, the method further comprisesremoving the temporary bonded semiconductor substrate from the transferdevice. In an example, the method further comprises forming an internalflow path to allow coolant to traverse there through to cool thetransfer device. The inter-layer coolant channels may be formed by useof a patterned photo resist layer added over the unpatterned photoresistlayer. The thickness and/or location of the patterned photo resist layermay be chosen to adjust the local penetration depth of the proton beamto form a non-planar cleave surface in the substrate containing the topsurfaces of the coolant channels, with the bottom surface provided bythe lower bond plane.

In an example, the plurality of transistor devices are selected from atleast one of CMOS devices, bipolar transistors, logic devices, memorydevices, digital signal processing devices, analog devices, lightabsorbing and imaging devices, photo-voltaic cells or micro-electricalmechanical structures (MEMS), or any combination thereof.

In an example, the implantation process, proton energy ranges from 500kilovolts to 2 MeV. In an example, the cleave region is positioned 1 to10 microns from a top surface of the dielectric material. In an example,the unpatterned photoresist material is selected with high absorptivityof electromagnetic radiation with a wavelength less than 400 nm. In anexample, the semiconductor substrate comprises a silicon or othersuitable material for formation of electrical, optical orelectromechanical devices.

In an example, the implantation process is provided at a dose rangingfrom 5E16 to 5E17 particles/centimeter². In an example, the implantationprocess is provided using a beam line implanter. In an example, theimplantation process is provided by a linear accelerator (LINAC) orother variation.

In an example, the cleave region having a peak concentration at an edgeof an implantation range. In an example, the cleave region comprises aplurality of hydrogen gas-filled micro-platelets. In an example, thecleave region is characterized by a stress sufficient to inducepropagation of an approximately planar cleave region. In an example, thecleave region is configured as a uniform implantation region or apatterned implantation region. In an example, the cleave region ispatterned or graded to facilitate a controlled cleaving action.

In an example, the method comprises forming a plurality of interconnectstructures between the backside surface and either the plurality oftransistors or the inter-connect region. In an example, the methodfurther comprises providing a second semiconductor substrate comprisinga plurality of second transistor devices and an overlying seconddielectric material; and bonding the second dielectric materialconfigured with the second semiconductor substrate to form a stackedsemiconductor structure. In an example, the method further comprisesforming a patterned photoresist material overlying the unpatternedphotoresist material.

In an example, the plurality of transistor devices and the interconnectregion are characterized by a thickness of three microns and less;wherein the implantation process is characterized by a range of fivemicrons to ten microns such that a characteristic size of the pluralityof transistor devices and the interconnect region does not influence theimplantation process. In an example, the plurality of transistor devicesand the interconnect region are characterized by a thickness of threemicrons and less; wherein the implantation process is characterized by arange of five microns to ten microns such that a characteristic spatialdimension of the range of the implantation is not interfered by thethickness of the plurality of transistor devices and the interconnectregion. In an example, the plurality of transistor devices is providedfor a memory array or a logic array.

In an example, the energy is selected from thermal, mechanical,chemical, electrical, or combinations thereof to provide a cleaveinducing energy. In an example, the energy is provided to cause acontrolled cleaving action including an initiation of cleaving andpropagation of cleaving. In an example, the energy is provided to form aplurality of micro-platelet bubbles in the cleave region. A cleavesurface may connect a network of the micro-platelet bubbles

The present disclosure achieves these benefits and others in the contextof known process technology. However, a further understanding of thenature and advantages of the present disclosure may be realized byreference to the latter portions of the specification and attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an embodiment of this disclosure.

FIG. 2 illustrates a heterogeneous structure containing a layer oftransistor devices and an upper network of metal and low-dielectricconstant materials, with provisions for inter-layer coolant channelsprovided by implantation through an additional, patterned photo resistlayer in an example.

FIGS. 2A-B are simplified cross-sectional views showing use of patternedoxide as an absorber.

FIG. 3 is a schematic view of the transferred device layer viewed at thepoint of non-uniform surface cleaving after proton implants throughpatterned dual-layer photoresist (PR) layers, viewed after removal ofthe PR layers and attachment of a temporary-bonded transfer holder in anexample.

FIG. 4 sketches a to-be-transferred IC device at the point of thehigh-dose proton implant with a uniform PR layer in place over thedevice metal interconnect layers in an example.

FIG. 5 is a simplified view of the transfer device layer after theproton implant, removal of the PR layer attachment of the temporarybonded transfer holder and completion of the wafer level cleavingprocess in an example.

FIG. 6 shows the major steps applied to the bottom region of thetransferred device layer comprising the formation of an oxide layersuitable for bonding after removal of the implant damage layer and finaladjustment of the device layer substrate layer thickness and formationof the dense array of inter-layer metal connections and bonding pads inan example.

FIG. 7 shows the cleaved and prepared transferred device layer at thepoint of precision alignment with mating interconnect structures on theupper surface of a lower device layer in the developing 3D device stackin an example.

FIG. 8 shows a completed intimate 3D stack of a transferred IC devicebonded to a lower device layer, with aligned inter-level metal lines inplace and bonded at landing pads along the oxide layer bond interface inan example.

FIG. 9 shows a schematic example of two device layers stacked with thickmetal interconnect layers in an example.

FIG. 10 shows one example of a process flow for preparing a separablesubstrate according to an embodiment.

FIG. 10A shows IC processing and/or thinning steps performed downstreamof the process flow shown in FIG. 10.

FIG. 11 shows a simplified view of a general IC process flow accordingto an embodiment.

FIGS. 12-15 show simplified processing flows according to variousalternative embodiments.

FIG. 16 is a simplified cross-sectional view showing a patterned high-Klayer in place, incorporating coolant channels.

FIG. 17A is a simplified cross-sectional view showing an example of adetached, unsupported, device layer, under net compressive stress afterits fabrication, on a thin substrate layer, deforming its thin substratelayer into a concave shape.

FIG. 17B is a simplified cross-sectional view of the effect of theaddition of a stress-compensating layer to the backside of a thinsubstrate containing a stressed device layer on the top side.

FIG. 18 is a simplified view of the bonding a high-purity, singlecrystalline transfer layer onto a chemically or mechanically “weak”separation layer on a substrate.

FIG. 19A shows a simplified cross-sectional view of high-energy, highdose proton implant to form a Hydrogen-rich layer placed several micronsbelow the CMOS transistor layer.

FIG. 19B is a simplified cross-sectional view of CMOS device layersafter completion of the formation of final gate stack and metalinterconnect structures, with a Hydrogen-rich layer formed by ahigh-energy, high-dose proton implant performed just prior to the“replacement gate” fabrication steps.

FIG. 20 shows a simplified cross-sectional view of a “top-to-top” metallayer bonding of a transfer device layer and a lower device layer in a3DIC stack.

FIG. 21 illustrates a process for forming a 3DIC structure withdifferent die sizes.

FIG. 22 is a simplified cross-sectional view showing an example of alower device structure.

FIG. 23 is a simplified cross-sectional view showing an example of astacked device structure.

FIG. 24 is a simplified cross-sectional view showing an example ofsmaller die size devices bonded on a 3DIC.

FIG. 25 is a simplified cross-sectional view showing an example ofmaterials deposited over smaller die size devices bonded on a 3DIC.

FIG. 26 is a simplified cross-sectional view showing an example of a3DIC structure with different die sizes.

FIG. 27 is a simplified cross-sectional view showing another example ofa 3DIC structure with different die sizes.

FIG. 28 is a simplified cross-sectional view showing an example ofproton implantation.

FIG. 29 is a simplified cross-sectional view showing an example ofproton implantation through a range compensating layer.

FIG. 30 illustrates thermal conductivity of a silicon substrate atvarious phosphorus dopant concentrations and temperatures.

FIG. 31 illustrates thermal conductivity of a silicon substrate atvarious boron dopant concentrations and temperatures.

FIG. 32 illustrates thermal conductivity according to temperature for6H-SiC at various temperatures and dopant concentrations.

FIG. 33 illustrates thermal conductivity of various carbon materials.

FIG. 34 illustrates a bonding step for a transfer layer.

FIG. 35 illustrates forming a buried Hydrogen profile below a partiallycompleted device layer.

FIG. 36 illustrates a complete device layer over the Hydrogen profile.

FIG. 37 illustrates 1 MeV protons implanted into a 3 μm thick multilayercontaining Cu metal and SiO₂ dielectric layers on a Si substrate with aCMOS device layer located just below the metal/oxide multilayer.

FIG. 38A and 38B respectively illustrate a recoil profile and anionization profile for the implantation of FIG. 37.

DETAILED DESCRIPTION OF THE SPECIFIC EXAMPLES

According to the present disclosure, techniques generally related to themanufacture of integrated circuit devices are provided. Moreparticularly, the present disclosure provides a method and resultingdevices for stacking and interconnecting three-dimensional (3-D) devicesusing heterogeneous and non-uniform layers, such as fully fabricatedintegrated circuits. By way of example, the integrated circuits caninclude, among others, memory devices, processor devices, digital signalprocessing devices, application specific devices, controller devices,communication devices, and others.

An embodiment builds and extends the capabilities of two large areas oftechnology, layer transfer methods for formation of bonded stacks ofhomogeneous layers, such as the formation of Silicon-on-Insulator (SOI)wafers and diverse methods in present use and development to form 3-Dstacks of electrical devices through the use of complex interposerlayers and sparse arrays of metal vias for inter-device connections.

An embodiment provides for methods of stacking and interconnection ofdiverse electrical and electro-mechanical layers with simplified bondand interconnect structures with physical scales that are a factor of 10or more smaller than presently available interposer/TSV methods andproviding for greatly increased number of inter-device electricalconnection paths, resulting in greatly expanded data transfer bandwidthand 3-D device functionality. The present disclosure also provides forprotection of sensitive device layers from harmful ultraviolet radiationassociated with the use of high-energy proton beam lines and forconstruction of inter-level networks of coolant flow channels forremoval of heat from the volume of the functions 3-D device stack.Further details of the present disclosure can be found throughout thepresent specification and more particularly below.

Embodiments may combine Silicon-On-Insulator (SOI) wafer formationapproaches utilizing techniques such as H-cut separation andplasma-activated bonding to achieve a room temperature transfer process,combined with Si separation utilizing MeV proton technology, to achievefull-CMOS 3D stacking.

Such Layer-Transfer (LT) applied to 3D Wafer-Scale Packaging (WSP) canallow substantial benefits due to its high parallel connectivity andability to use different processes. Embedded RAM/Cache layers are anatural application.

Conventional WSP approaches may experience challenges in one or more ofthe various areas of: bonding, layer alignment, layer thinning, andlayer strata interconnect. For example, layer thinning to less than 10μm can desirably lead to vias with smaller aspect ratios.

Use of plasma fusion bonding allows favorable alignment. And,embodiments as described herein may make layer alignment andinterconnect practically achievable goals.

Embodiments utilizing LT technology involving cold processing, allowprocessing of wafers with Interlayer Dielectric (ILD)/metalinterconnects. The plasma-activated fusion bond confers bond strength,ultra-thin bond, no glue layers. As described below, fast thinningoperation is possible, without necessarily requiring chemical mechanicalpolishing (CMP), polishing, or grinding operations.

Embodiments may be compatible with a variety of IC processes, includingthose used to fabricate complementary metal oxide semiconductor (CMOS)and Random Access Memory (RAM) devices, etc.

The use of implantation at MeV energies allows thicker implantationthrough an entire device layer (10 μm). Thus, a full CMOS device layercan be transferred instead of partial layers.

Implant scanning techniques may be used. Examples can include obtainingchanneling improvements through “dithering”.

Utilization of MeV protons by embodiments for full CMOS stacking, mayoffer certain benefits. Embodiments may allow avoidance of shadowing dueto CMOS layers that include transistor, dielectric, and/or metal layerstructures.

A 1 MeV proton beam is sufficient to perform H-cut implants through 8 Cumetal interconnect layers and a full-depth CMOS microprocessor unit(MPU) with ≈10 μtm Si penetration.

Such a 10 μm depth in Si, for a 1 MeV proton beam through a model8-layer Cu interconnect array and connected CMOS transistor layer, ismore than adequate for separation of damage peak from CMOS deviceregion. A figure of merit for the desired minimum separation below theCMOS transistor layer of the proton damage region and bond oxide surfaceof the transferred layer substrate layer is the depletion depth into thesubstrate material of a biased, powered on, bulk CMOS array, on theorder of 1 micrometer for a 1 V supply voltage and a 10 Ohm-cm substratematerial. CMOS transistor layers comprising bulk “finFET” and“fully-depleted SOI” devices can have somewhat thinner substratedepletion thickness, depending on the device design and supply voltage.Relative precision (straggling/range) of 1 MeV proton profiles is muchsharper than standard SOI wafer fabrication implants (at ≈40 keV).

It is further noted that H peak depth can be reduced by spin-on resistabsorber layers. This aspect is further described in connection withFIGS. 1-9 discussed later below.

FIG. 10 shows one example of a process flow 1000 for preparing aseparable substrate according to an embodiment. Here, a donor substrate1002 is subjected to cleave plane formation 1004, e.g., by theimplantation of hydrogen ions.

Then, the donor substrate including the cleave plane is bonded to ahandle substrate 1006, e.g. by a plasma-activated bonding process 1008.Next, the LT occurs by the performance of a room Temperature—ControlledCleaving Process (rT-CCP™), such that a portion of the donor remainswith the handle substrate. Alternatively, a portion of the donor mayremain with a temporary carrier substrate if this layer is to beretransferred again to a permanent handle substrate (e.g., for back sideillumination CMOS image sensors).

The remaining portion of the donor substrate is reclaimed 1011 forfurther use. The handle including the transferred layer 1010 may besubjected to further processing—e.g., epitaxial (EPI) smoothing andthickening 1012, to produce the separable substrate 1014.

FIG. 10A shows a simplified process flow 1050 illustrating downstreamsteps performed upon the substrate provided by a substrate manufacturerof FIG. 10. Those steps may comprise IC processing 1052 (see, e.g., FIG.11 below) and/or thinning 1054 (see, e.g., FIGS. 12-15 below).

Specifically, FIG. 11 shows a simplified view of a general IC processflow 1100 according to an embodiment. Here, the IC Maker received“special wafer” 1102 and processes IC layer “n+1” 1104 without anymodifications.

Then, the IC layer is bonded onto the Wafer Scale Processing (WSP) stack(1 to n) 1106. After bonding, the wafer 1102 can be released.

Shown last in FIG. 11 is the performance of steps to such asinterconnect processing, Chemical Mechanical Polishing (CMP), etc. tofinish a layer 1108. This can be repeated for a layer “n+2”.

At least four layer transfer (LT) packaging variants are possible. FIGS.12-15 describe four options of LT for thinning.

FIG. 12 shows an embodiment of LT after IC processing. The simplifiedprocess flow 1200 shown in this figure involves putting a cleave plane1202 within the substrate 1203, and then cleaving 1204 after ICprocessing 1206. It requires more intrusive post-IC process steps.

FIG. 13 shows an embodiment utilizing cleave onto an etchable substrate.The simplified process flow 1300 according to this embodiment allows thesubstrate 1302 to be more easily etched 1304 than SOI bond-grind backprocesses.

In such embodiments, the etchable substrate may be thin. Anelectrostatic (ES) chuck can be used to help stiffen cleave and handlethe thin substrate. Transparent substrates can help with layeralignment.

FIG. 14 shows an embodiment of a process flow 1400 where the substrate1402 comprises a “thin” substrate attached to a releasable basesubstrate. The thin substrate can be utilized in the final 3D product.The releasable substrate is solely used for handling during the ICprocess.

FIG. 15 shows a simplified process flow 1500 according to anotherembodiment. Here, the silicon film 1502 is mounted to a releasablesubstrate 1504. The releasable substrate is solely used for handlingduring IC process 1506 resulting in processed layer 1508. An internalrelease layer is used after LT. The release layer is put within the bondplane. LT is used to release the processed Si-layer, followed bythickening if necessary.

Certain features and benefits may accrue with one or more embodiments.For example, H-cut splitting and layer transfer techniques may beextended to beyond lamination of uniform composition layers to enablewafer-scale stacking of heterogeneous and non-uniform individual layers,with the specific application of intimate stacking of fully-fabricatedintegrated circuits, including transistor layers and multi-layerinterconnect networks.

Embodiments may achieve high data transfer bandwidth with high-densityinter-die interconnect with thin device stacking using “intimatebonding” with H-cut and layer transfer techniques.

Embodiments may increase manufacturability and device yield by use ofroom to modest-temperature process throughout the stacking process.

Some implementations may outline device layer lamination with H-cut andplasma-bonding operations (using high-alignment accuracy bonding tools).

Particular embodiments may utilize variations on front-back stack andfront-front stack bonding, with corresponding interconnect depths andlocations.

Some embodiments may thin total device layer elements (no need forinterposers), with decreases in RC losses even for high-densityinter-device via connections.

Various embodiments may lower stress via connections with much reduced“keep out” area from Cu/Si stress.

Certain embodiments may implement methods for post-splitting damagelayer removal and substrate thickness reduction (selectiveetching)—appropriate for bonding and heat transfer requirements (muchless stringent than SOI wafer layer lamination).

Certain additional factors of particular embodiments are also nowdescribed. Some such factors may deal with non-uniform totalCu-interconnect thickness in various IC designs.

For example, metrology can be used. A scan effect of non-uniform Cudensity collects backscattered proton current from a large-anglecollection electrode facing IC metal surface with a≈1×1 um² aperture forMeV proton beam. A precision stage scanner for IC motion under aperturemaps out net Cu density by backscatter current.

Design rules can be used to address non-uniformity. These design rulesmay specify allowable variations in total Cu thickness across IC deviceareas. Wafer-level splitting can be achieved with large-areacheckerboard H distributions.

A manufacturing process can be used to address non-uniformity. Forexample, a “dummy” Cu or other similar material layer may be added atpositions of low-Cu thickness, such as inter-layer metal via channels.Examples of other materials include materials such as CVD-depositedoxide and nitride dielectrics, polymers, and other metals. In general,the material should have sufficient ion stopping power and thickness tobring the location of deep proton peaks into an approximately similardepth across a cleave plane.

Embodiments may set the cleave plane depth, not directly affected byproton energy or variation in total Cu-layer densities, by constructingIC devices over a high-stress epi layer, such as a graded Si-Ge thinlayer, to localize post-stopping H concentration along high-stressinterfaces. The cleave plane will be set by the location of thehigh-concentration H distribution accumulated at the built inhigh-stress interface.

Total proton dose and related risk of dielectric bond damage (in low-kinterconnect and high-k gate dielectrics) from electronic stoppingevents may be reduced, by increasing proton lattice damage accumulation(via nuclear stopping events) by lowered wafer temperature during protonimplantation.

1A. A method, comprising:

-   -   providing a first substrate having dielectric structures and        conductive structures;    -   implanting ions into the first substrate, the ions traveling        through the dielectric structures and the conductive structures        to define a cleave plane in the first substrate; and    -   cleaving the first substrate at the cleave plane to obtain a        cleaved layer having the dielectric structure and the conductive        structures,    -   wherein the cleaved layer is used to form a three-dimensional        integrated circuit device having a plurality of stacked        integrated circuit (IC) layers, the cleaved layer being one of        the stacked IC layers.

The method of clause 1A, wherein the implantation is performed whilekeeping the first substrate at a temperature of 100 degrees Celsius orless.

In one embodiment, the implantation is performed at room temperature.

The method of clause 1A, wherein the implantation energy is greater than100 KeV and the ions are protons.

The method of clause 3A, wherein the implantation energy is 300 KeV orgreater.

The method of clause 3A, wherein the implantation energy is 500 KeV orgreater.

The method of clause 3A, wherein the implantation energy is 1 MeV orgreater.

The method of clause 1A, wherein the dielectric structures and theconductive structures are formed on the first substrate by performing aplurality of processing steps on the first substrate.

As mentioned above, certain embodiments may reduce H peak depth byspin-on resist absorber layers. This is now discussed below.

FIG. 1 is a schematic view of an embodiment at completion of atwo-device 3D stacking process. The upper device layer, containingheterogeneous layers of transistors formed in semiconductor materials,usually Si, and a dense network of metal, usually Cu with various othermetals for liners and vias, layers separated by low-dielectric constantelectrical insulator materials, is separated from a semiconductor waferafter formation processing by hydrogen implant and associated cleavingprocess. During proton implant, the transfer device structure is coveredwith a uniform photoresist layer of sufficient thickness and propertiesto protect the device layers from damaging exposure to ultra-violetradiation from recombination processes in the proton beam line plasma.For the case shown in FIG. 1, the transferred device layer is alsocoated with a second photoresist layer patterned to adjust the depth ofthe proton beam and the resulting cleave surface along the paths of anetwork of coolant flow channels designed to remove heat from the volumeof the completed 3-D device stack. Conductive structures includetransistor junctions in the substrate and a metal interconnect networkcontacted to the transistor layer.

After mounting of the upper device layer to a temporary bond handlewaver, the cleaved lower surface of the transfer device is processed toremove implant damage in the region of the cleave surface and adjust thethickness of the transfer device substrate layer. Then a CVD oxide layeris deposited on the lower surface to provide an efficient bondingsurface and to provide an electrically insulating and passivated surfacefor the coolant flow channels, if present. The lower device surface isthen etched and filled with metal to form inter-level electricalconnection to the transfer device interconnect layers, through asubstrate and deposited oxide layer thickness of the order of 1 or moremicrons. The inter-level metal lines in upper transfer device layers areterminated with metal bond pads with bond surfaces at the same plane asthe deposited oxide bonding layer.

A similar deposited oxide is formed on the lower device top surface toprovide efficient bonding, a network of vias are etched and filled withmetal to provide electrical connections with the lower deviceinterconnect layers. The lower metal lines are terminated by metal bondpads at the same plane as the lower deposited oxide surface.

The two sets of metal bonding pads are aligned in a precision bondingapparatus and subjected to bond anneal processing, completing the2-level stack shown in FIG. 1 (with coolant channels).

FIG. 2 shows a view of patterned PR and device layer after layertransfer to lower device layer. In FIG. 2, a heterogeneous structurecontaining a layer of transistor devices and an upper network of metaland low-dielectric constant materials providing interconnects for anintegrated circuit (IC) is coated with a uniform photoresist (PR) layer,where the resist properties and thickness is chosen to provide adequateprotection for sensitive IC layers and interfaces from exposure toultra-violet (wavelength less than 400 nm) radiation arising fromrecombination events in the proton accelerator beam line plasma. Thethickness and stopping of the uniform PR layer is also chosen to adjustthe range of the proton beam to a desired depth below the IC devicetransistor and depletion layers.

In FIG. 2, a second, patterned, PR layer is added over the uniform PRlayer with the thickness and stopping of the second PR layer chosen tolocally adjust the depth of the implanted proton distribution to providea non-planar material splitting surface. When the transferred devicelayer is bonded to a lower device layer, after removal of the PR layersand temporary bonding to a holder layer, the non-planar splittingsurface provides a network path, reflecting the patterning of the upperPR layer, for flow of coolant in the finished IC device stack forremoval of heat during device operation.

Also shown in FIG. 2 are inter-level metal vias and bonding landing padsand oxide bonding interfaces which are added to the lower section of theupper transferred device layer before bonding to the lower devicelayers, described in more detail in later figures.

Top absorber layers may be used to (1) locally control the depth of thepeak of the proton damage profile in the transfer device substrate,thereby controlling the location of cleave surface at separation; (2)define the lateral location and depth of coolant channels formed by thedepth variations in the cleave surface; and/or (3) provide a protectivelayer to absorb UV-radiation arising from electron capture andsubsequent radiative processes by proton ions in the accelerator beamline.

Certain embodiments of this process use an un-patterned, cross-linkedphoto-resist (PR) layer with a second PR layer deposited above,lithographically exposed and developed to leave a patterned PR overlayer.

Other embodiments of this process may use CVD deposited dielectricfilms. In certain embodiments, an un-patterned CVD oxide layer isdeposited on the top surface of the metal interconnect network of thedevice layer to be transferred to the 3DIC stack. The thickness of thisfirst CVD oxide layer may be chosen so that the combined stopping powereffects of the CVD oxide, device metal interconnect network and thedevice substrate places the proton and damage peaks at the desired depthof the main cleave plane surface below the transfer device transistorlayer.

A CVD nitride layer is then deposited on the first CVD oxide layer toact as an etch stop to protect the underlying oxide layer during theetching of the top CVD oxide layer.

Then a second CVD oxide layer is deposited on the nitride layer. Thethickness of the top CVD oxide layer may be chosen to locally shift thelocation of the peak of incident proton beam to be shallower than thelocation of the main cleave surface by the desired height of coolantflow channels to be formed by the subsequent bonding of the transferreddevice layers to a planar bonding surface on the top of an underlyingdevice layer in the 3DIC stack.

A PR layer may then be deposited on the top oxide, lithographicallyexposed and developed to leave a patterned PR over-layer. This patternedPR layer protects the top CVD oxide layer in the locations where thecoolant channels will be formed during the subsequent oxide etch step,with the nitride layer protecting the lower oxide layer.

FIG. 2A is a simplified cross-sectional view of the transfer devicelayer at proton implant showing an un-patterned top CVD layer withthicknesses chosen to shift the peak of the proton profile to be at adepth of the desired location of the cleave surface. A patterned secondCVD oxide layer, with thickness chosen to shift the proton beam peak tothe height of the (optional) coolant channels to be formed during thesubsequent bonding step to the 3DIC device stack. A CVD nitride layerdeposited between the two oxide layers act as an etch stop for the topoxide patterning etch.

FIG. 2B is a simplified view of upper layers of the transfer deviceafter deposition of un-patterned CVD oxide and nitride layers,deposition of a top CVD oxide and PR layers. After lithographic exposureand development of the PR pattern, exposed top CVD layer material isetched off. The nitride layer protects to the lower CVD layer from etchremoval. The PR layer is removed prior to proton implant.

The use of CVD dielectric layers to form the top absorber layers mayoffer the manufacturing benefit of avoiding the process complicationsthat accompany high-energy implants through polymer PR films, such asout-gassing of Hydrogen and other volatile materials due to thebond-breaking in the PR materials by collisions with the passing protonbeam.

The local control of the proton implant profile into the device andsubstrate layer through the use of patterned and un-patterned CVD toplayers can be used to compensate for local variations pattern densityand total layer thickness in metal interconnect networks both acrosscomplex chip die and for processing diverse chip designs on in-process,large-area wafers. This capability for local control on the protonprofile depth and location of the cleave surface at separation enablesthe use of a constant energy proton beam for processing of diversedevice types, improving in-line wafer manufacturing efficiency.

FIG. 3 is a schematic view of the transferred device layer viewed at thepoint of non-uniform surface cleaving after proton implants throughpatterned dual-layer PR layers, viewed after removal of the PR layersand attachment of a temporary-bonded transfer holder. Following thenon-uniform surface splitting, the damaged material surrounding thecleave planes, containing H-filled platelets and adjacent lattice damageregions, is removed and additional bottom layer material is removedleaving the desired depth of substrate material containing the IC devicetransistor and depletion regions.

In addition, the non-planar splitting surface is then treated withdeposited oxide films to form passivated surface walls for coolantchannels as well as formation of efficient bonding surfaces forattachment to adjacent device layers. The lower region of thetransferred device layer is also processed to form inter-layer metalconnection paths between the device layers, described in later figuresand discussions.

FIGS. 4 through 9 illustrate the 3D stacking process for a generic setof IC layers using a uniform top PR layer, with no provisions forincorporated coolant channels, for simplicity. Further details of thesedrawings can be found throughout the present specification and moreparticularly below.

FIG. 4 sketches a to-be-transferred IC device at the point of thehigh-dose proton implant, with a uniform PR layer in place over thedevice metal interconnect layers. The metal interconnect layers aretypically a densely patterned, multi-layer structure, comprising 10 to15 layers of Cu metal, for advanced logic devices, less for memorydevices. The Cu metal layers and vias are electrically isolated byinterleaved layers of low-dielectric constant insulating materials. Thenet Cu layer thickness is typically 3 microns or less in modernpractice, without the 5 to 8 micron thick metal layers used for accuratedistribution of device synchronization, or “clock”, signals, power andground. Provisions for additional of thick metal interconnects areoffered as part of the inter-level stacking process.

The density, optical properties and thickness of PR are chosen toprovide adequate protection of the underlying device layers fromexposure to UV-wavelength recombination radiation from the protonaccelerator beam line plasma and to adjust the depth of the proton peakand cleave plane below the transistor doping and depletion layers.

A view of the transfer device layer after the proton implant, removal ofthe PR layer attachment of the temporary bonded transfer holder andcompletion of the wafer level cleaving process is shown in FIG. 5. Thecleaving action can be effected by local application of energy in theform of mechanical, chemical, laser or other thermal exposure or globalenergy or any combination thereof. Cleaving can occur using any of thetechniques disclosed in the '563 Patent, which had been incorporated byreference, a blister technique, or others.

FIG. 6 shows the major steps applied to the bottom region of thetransferred device layer which include removal of proton-damagedmaterial in the immediate vicinity of the cleave plane as well as anyadditional material in order to obtain the desired transfer substratethickness, formation by chemical vapor deposition (CVD) of a planarbonding interface and formation of inter-level metal lines connectingthe transferred device metal interconnect network with lower bondingpads at the plane of the deposited bonding oxide interface. Inter-layervia formation is shown.

FIG. 7 shows the cleaved and prepared transferred device layer at thepoint of precision alignment with mating interconnect structures on theupper surface of a lower device layer in the developing 3D device stack.An embodiment exploits the capabilities of advanced alignment andbonding apparatus with wafer level alignment tolerances in the range of150 nm for 300 mm wafers. Vias and via landing pads are shown.

FIG. 8 shows a completed intimate 3D stack of a transferred IC devicebonded to a lower device layer, with aligned inter-level metal lines inplace and bonded at landing pads along the oxide layer bond interface.Also shown in FIG. 8 is a top deposited oxide layer with metal vias andlanding pads at the bond interface level for subsequent stacking of anadditional device layer on top of the present transferred device layer.

For 3D stacking of large-area, high performance logic IC devices,accurate delivery of power, clock and signal pulses requirelow-resistance paths provided by several micron thick metal lines. Thesemetal layers are too thick to be implanted through with modest (1 or 2MeV) energy proton beams but can be provided for, where needed, as partof the inter-level processing post implant and cleaving and before thestacking of subsequent device layers. FIG. 9 shows a schematic exampleof two device layers stacked with thick metal interconnect layers, thepower device with the completed metal layers in place if it is thebottom device layer and the upper transferred device with the thickmetal interconnects added after device transfer and permanent bondingand before the deposition of bonding oxide and formation of inter-levelmetal lines and bond landing pads. The dual device stack hasincorporated thick metal clock & power distribution layers.

The discussion here is in terms of a stack of generic CMOS devices. Auseful example is a stack of extended memory elements connected to adata transfer layer for high-bandwidth signal processing andcomputation, such as memory stacks presently formed with the use ofinterposer layers and metal connection lines, known as Through-Siliconvias (TSVs), with length of the order of 30 to 50 microns, over 10 timeslonger than the inter-level connections envisioned in an embodiment.

The utility of embodiments can be exploited to provide fabricationmethods for intimate 3-D stacks of diverse electrical andelectro-mechanical devices incorporating heterogeneous device layers forsensing of visual images, chemical environments and diverse physicalconditions combined with stacked integrated circuits to provide signalprocessing, memory and data transmission in an integrated and robust 3-Ddevice.

Although the above description is in terms of a silicon wafer, othersubstrates may also be used. For example, the substrate can be almostany monocrystalline, polycrystalline, or even amorphous type substrate.Additionally, the substrate can be made of III/V materials such asgallium arsenide, gallium nitride (GaN), and others. The multi-layeredsubstrate can also be used according to an embodiment. The multi-layeredsubstrate includes a silicon-on-insulator substrate, a variety ofsandwiched layers on a semiconductor substrate, and numerous other typesof substrates. One of ordinary skill in the art would easily recognize avariety of alternatives, modifications, and variations.

1B. A method for fabricating an integrated circuit, the methodcomprising:

providing a semiconductor substrate comprising a surface region, aplurality of transistor devices formed overlying the surface region, aninterlayer interconnect region comprising a structured metal layer and astructured dielectric layer and an inter-layer connection overlying theplurality of transistor devices, and a dielectric material overlying theinterconnection region to provide a bonding interface;

forming an unpatterned photoresist material overlying the bondinginterface provided from the dielectric material, the unpatternedphotoresist material is configured to shield one or more of theplurality of transistors from electromagnetic radiation in a wavelengthrange of below 400 nm and to selectively adjust a depth of a subsequentimplanting process;

subjecting the unpatterned photoresist material to the implantationprocess to introduce a plurality of hydrogen particles through theunpatterned photoresist material to a selected depth to a cleave regionunderlying the surface region of the semiconductor substrate to define atransfer device between the cleave region and a surface of thedielectric material to form a thickness of a multi-layer of a pluralityof interconnected conductive metal layers and insulating dielectrichaving a total metal thickness of 3 to 5 microns or less;

removing the unpatterned photoresist material after the hydrogen implantstep;

bonding the surface of the dielectric material overlying the transferdevice to a transfer substrate to temporarily bond the semiconductorsubstrate to the transfer substrate;

subjecting sufficient energy to a portion of the cleave region to removean upper portion of the semiconductor substrate from a lower bulksubstrate material, while using the transfer substrate to hold the upperportion of the semiconductor substrate such that the upper portioncomprises a hydrogen damaged region;

subjecting the hydrogen damaged region overlying the transfer device toa smoothing process to remove a portion or all of the portion or all ofthe hydrogen damaged region and to form a backside surface; and

forming a thickness of dielectric material overlying the backsidesurface.

2B. The method of clause 1B wherein the backside surface is configuredwith one or more provisions for formation of an inter-layer conductivepath to linking to a bottom landing pad in the structured metal layer ofthe transfer device and a landing pad for a bonded conductive path to anadjacent device layers.

3B. The method of clause 2B further comprising depositing a dielectriclayer to form a suitable bonding interface on the structured metallayer, the structured metal layer comprising a 5 to 10 microns thickconducting layer formed over a densely patterned metal interconnectmulti-layers for provision of a device power signal, a ground signal anda frequency synchronization signal, and the dielectric layer having aplurality of conductive paths through the dielectric layer for bondingwith inter-layer conductors in an upper, transfer device layer.

4B. The method of clause 3B further comprising aligning of the transferdevice layer to the semiconductor substrate to permanently bond theinter-layer conducting path.

5B. The method of clause 4B further comprising removing the temporarybonded semiconductor substrate from the transfer device.

6B. The method of clause 5B further comprising forming an internal flowpath to allow coolant to traverse there through to cool the transferdevice.

7B. The method of clause 1B wherein the plurality of transistor devicesare selected from at least one of CMOS devices, bipolar transistors,logic devices, memory devices, digital signal processing devices, analogdevices, light absorbing and imaging devices, photo-voltaic cells ormicro-electrical mechanical structures (MEMS), or any combinationthereof.

8B. The method of clause 1B wherein implantation process ranges from 500kilovolts to 2 MeV.

9B. The method of clause 1B wherein the cleave region is positioned 1 to10 microns from a top surface of the dielectric material.

10B. The method of clause 1B wherein the unpatterned photoresistmaterial is selected with high absorptivity of electromagnetic radiationwith a wavelength less than 400 nm.

11B. The method of clause 1B wherein the semiconductor substratecomprises a silicon or other suitable material for formation ofelectrical, optical or electromechanical devices.

12B. The method of clause 1B wherein the implantation process isprovided at a dose ranging from 5E16 to 5E17 particles/centimeter².

13B. The method of clause 1B wherein the implantation process isprovided using a beamline implanter.

14B. The method of clause 1B wherein the implantation process isprovided by a linear accelerator (LINAC) process.

15B. The method of clause 1B wherein the cleave region having a peakconcentration at an edge of an implantation range.

16B. The method of clause 1B wherein the cleave region comprises aplurality of hydrogen gas-filled micro-platelets.

17B. The method of clause 1B wherein the cleave region is characterizedby a stress sufficient to induce propagation of an approximately planarcleave region.

18B. The method of clause 1B further comprising forming a plurality ofinterconnect structures between the backside surface and either theplurality of transistors or the inter-connect region.

19B. The method of clause 1B further comprising providing a secondsemiconductor substrate comprising a plurality of second transistordevices and an overlying second dielectric material; and bonding thesecond dielectric material configured with the second semiconductorsubstrate to form a stacked semiconductor structure.

20B. The method of clause 1B further comprising forming a patternedphotoresist material overlying the unpatterned photoresist material.

21B. The method of clause 1B wherein the cleave region is configured asa uniform implantation region or a patterned implantation region.

22B. The method of clause 1B wherein the plurality of transistor devicesand the interconnect region are characterized by a thickness of threemicrons and less; wherein the implantation process is characterized by arange of five microns to ten microns such that a characteristic size ofthe plurality of transistor devices and the interconnect region does notinfluence the implantation process.

23B. The method of clause 1B wherein the plurality of transistor devicesand the interconnect region are characterized by a thickness of threemicrons and less; wherein the implantation process is characterized by arange of five microns to ten microns such that a characteristic spatialdimension of the range of the implantation is not interfered by thethickness of the plurality of transistor devices and the interconnectregion.

24B. The method of clause 1B wherein energy is selected from thermal,mechanical, chemical, electrical, or combinations thereof to provide acleave inducing energy.

25B. The method of clause 1B wherein the energy is provided to cause acontrolled cleaving action including an initiation of cleaving andpropagation of cleaving.

26B. The method of clause 1B wherein the energy is provided to form aplurality of micro-platelet bubbles in the cleave region.

27B. The method of clause 1B wherein the plurality of transistor devicesis provided for a memory array or a logic array.

28B. The method of clause 1B wherein the cleave region is patterned orgraded to facilitate a controlled cleaving action.

29B. A method for fabricating an integrated circuit, the methodcomprising:

providing a semiconductor substrate comprising a surface region, aplurality of transistor devices formed overlying the surface region, aninterlayer interconnect region comprising a structured metal layer and astructured dielectric layer and an inter-layer connection overlying theplurality of transistor devices, and a dielectric material overlying theinterconnection region to provide a bonding interface;

forming an absorber material overlying the bonding interface providedfrom the dielectric material, the absorber material configured to shieldone or more of the plurality of transistors from electromagneticradiation in a wavelength range of below 400 nm and to selectivelyadjust a depth of a subsequent implanting process;

subjecting the absorber material to the implantation process tointroduce a plurality of hydrogen particles through the absorbermaterial to a selected depth to a cleave region underlying the surfaceregion of the semiconductor substrate to define a transfer devicebetween the cleave region and a surface of the dielectric material toform a thickness of a multi-layer of a plurality of interconnectedconductive metal layers and insulating dielectric having a total metalthickness of 3 to 5 microns or less;

removing the absorber material after the hydrogen implant step;

bonding the surface of the dielectric material overlying the transferdevice to a transfer substrate to temporarily bond the semiconductorsubstrate to the transfer substrate;

subjecting sufficient energy to a portion of the cleave region to removean upper portion of the semiconductor substrate from a lower bulksubstrate material, while using the transfer substrate to hold the upperportion of the semiconductor substrate such that the upper portioncomprises a hydrogen damaged region;

subjecting the hydrogen damaged region overlying the transfer device toa smoothing process to remove a portion or all of the portion or all ofthe hydrogen damaged region and to form a backside surface; and

forming a thickness of dielectric material overlying the backsidesurface.

30B. The method of clause 29B wherein the absorber material comprisesphotoresist.

31B. The method of clause 29B wherein the absorber material comprisesoxide.

32B. The method of clause 31B wherein the oxide comprises CVD siliconoxide.

33B. The method of clause 29B wherein the absorber material comprises apatterned layer over an unpatterned layer.

34B. The method of clause 33B wherein a thickness of the unpatternedlayer shifts a peak of the proton profile to be at a depth of thedesired location of a cleave surface, and a thickness of the patternedlayer shifts the peak to a height of a coolant channels to be formed.

35B. The method of clause 29B wherein the absorber material comprisesnitride.

Generally, high-performance logic devices generate heat in regions ofhigh switching activity in the logic core. These sources of switchingheating are well known design concerns in complex system on a chip (SOC)and central processing unit (CPU) devices. The retention of data inmemory devices is generally degraded with increasing temperature, so theintegrated stacking of logic and memory layers is challenged by thesethermal concerns. Thermal controls become more important as the densityand diversity of the 3D device stack increases.

While beneficial for thermal bonding efficiency, use of oxide layers inthe bonding stack may be limited as a heat transfer layer by therelatively low thermal conductivity of SiO₂. The use of higher thermalconductivity, electrically insulating materials as inter-layerstructures can increase the heat transfer from local device thermalsource regions.

Accordingly, in certain embodiments it may be desirable to addstructured high-thermal conductivity layers between heat generatingdevice layers, in order to facilitate thermal spreading and removal ofheat from the device stack. Specifically, using high-energy protonimplantation, low-thermal budget layer cleaving and transfer bonding,may facilitate heat spreading from local device structure “hot spots”and efficiently remove device thermal energy through the use of localcoolant flows.

Proton cleaving and layer transfer methods, combined with the patternedcleave regions formed by use of a patterned top layer of photo-resist(or oxide as discussed below) at the proton implant step, bonded to aplanar device surface to form inter-layer channels for stack coolantflows, and the use of inter-layer structures with high-thermalconductivity (and low electrical conductivity), provide flexible designelements for controlling the thermal environment in a complex 3D devicestack.

Comparing the thermal conductivity of a variety of common semiconductormaterials indicates a variety of materials with substantially higherthermal conductivity than SiO₂, with SiC and Al₂O₃ (sapphire) comprisingcandidates for this purpose. Other high thermal conductivity materialsmay also be used for the purpose enhancing heat spreading and transportby factors of ≈10 to ≈100, compared to equivalent SiO₂ layers.

The following Table 1 lists thermal conductivity (in W/m-K) of severalcommon semiconductor and insulator films:

-   -   Si: 130 (W/m-K)    -   SiO₂: 1.3 (W/m-K)    -   SiC: 120 (W/m-K)    -   Ge: 58 (W/m-K)    -   GaAs: 52 (W/m-K)    -   Al₂O₃: 30 (W/m-K)

Inter-layer thermal spreading layer thickness of ≈0.5 to 2 um, may beexpected for efficient heat flows.

FIG. 16 shows a simplified cross-sectional view including a high-K layerin place, incorporating coolant channels.

1C. An apparatus comprising:

a first integrated circuit including a first metal interconnect layer;

a second integrated circuit including a second metal interconnect layer;and

an inter-layer structure including a high-thermal conductivity, lowelectrical conductivity material and bonded to the first metalinterconnect layer by a CVD oxide bond layer.

2C. An apparatus of clause 1C wherein the inter layer structure furthercomprises inter-layer channels for stack coolant flows.

3C. An apparatus of clause 1C wherein the high-thermal conductivitymaterial exhibits a thermal conductivity greater than 1.3 (W/m-K).

4C. An apparatus of clause 1C wherein the first integrated circuit isformed by proton implant into the first metal interconnect layerfollowed by cleaving.

Integrated circuit devices, containing diverse layers of semiconductor,dielectric and metal materials, may develop substantial internalstresses during fabrication. Unaddressed, these stresses may besufficiently high to warp full thickness Si wafers, with thicknessgreater than 700 micrometers, into a variety of concave, convex, andcomplex “potato chip” shapes. These deformations may be sufficientlylarge to create issues in fine-line lithography optics during devicefabrication.

If a stress-containing device layer on a detached thin (e.g., severalmicrometers) substrate were placed in an unsupported fashion on a planarsurface, the stress-induced deformation of a wafer-scale combinationcould pose a challenge for bonding to a planar substrate surface.Because of these effects, thin device layers may be attached to stiffbonding structures, capable of maintaining a planar bond interface withthe stressed layer attached, before they are detached from their initialsubstrate wafers.

FIG. 17A shows a simplified view of an example of a detached,unsupported, device layer, under net compressive stress after itsfabrication, on a thin substrate layer, deforming its thin substratelayer into a concave shape. Actual device layer deformations can be inconcave, convex, and complex “potato chip” shapes. These deformationscan lead to challenges when bonding to a planar surface as well as tobond failures and device degradation due to excess local stresses duringsubsequent thermal cycles during additional fabrication steps and duringdevice operation.

Even with the use of a stiff temporary bond holder to form astress-containing layer into a planar form suitable for bonding,un-compensated stresses in a complex bonded stack can lead to bondfailures and IC device degradation from thermal stress during subsequentfabrication steps and during device operation.

Accordingly, embodiments may provide for the addition ofstress-compensating layer(s) to the back side of stressed device thintransfer layers to facilitate a bonding process, including improvedinter-layer device and bond pad alignment, and to compensate fordeleterious effects of subsequent fabrication and device operationthermal cycles. U.S. Pat. No. 7,772,088 is hereby incorporated byreference for all purposes.

The backside stress compensation materials can be chosen of materialswith complementary thermal expansion properties to the device layer andwith thickness sufficient to offset the distortion effect of the devicestructure internal stress

FIG. 17B is a simplified cross-sectional view showing the effect of theaddition of a stress-compensating layer to the backside of a thinsubstrate containing a stressed device layer on the top side. The roleof the stress-compensating backside layers is to (1) facilitate bondingto a planar bond surface, (2) improve bond pad alignment accuracy duringwafer-level bonding, and/or (3) counteract the effects of differentialthermal stress during subsequent fabrication steps and during devicestack operation.

The stress compensating layers can be formed by direct layer transfer tothe transfer device layer backside while the transfer device layer isattached to temporary bonding structure. In some cases, a stresscompensating layer can be deposited by CVD or other approaches.

Note that the planar, stress compensated, transfer layer can provide adesirable geometry for achieving a high degree of bond pad alignmentduring wafer level bonding, which is one consideration for successfulwafer-level bonding for 3DIC manufacturing.

Embodiments may employ single crystal layer transfer onto chemical ormechanically “weak” separation layers. In particular, it may bedesirable to allow attaching a high-purity, single crystalline materiallayer onto a temporary holding layer that is sufficiently robust tosurvive the thermal, chemical and mechanical stresses of IC or otherdevice fabrication processes, but is “weak” enough to form a separationpath under directed chemical or mechanical action.

Examples of these weak temporary separation layers can include but arenot limited to (1) oxide layers formed by thermal growth, CVD depositionor by direct implantation and subsequent thermal processing, that canform a separation path under an overlying layer by chemical action of aselective etchant, such as HF attack on an underlying SiO2 layer, and(2) various forms of poly-crystalline or porous forms of the generalsubstrate material that are susceptible to form a separation path underselected chemical or mechanical attack. Forms of directed mechanicalattack can include but are not limited to, (1) stress-assisted crackformation initiated by a laterally directed force on a separatingwedge-shaped tool, and (2) kinetic attack by laterally directed fluidjets into a mechanically weak layer, such as a porous substrate materialregion.

Some forms of chemically or mechanically weak separation layers may lackthe high-level crystalline interface required for epitaxial growth ofhigh-purity and high-quality crystalline upper layers useful forfabrication of high performance semiconductor devices.

Employing high-energy proton implants to form Hydrogen-rich layers formechanical, room-temperature separation along well-defined cleavesurfaces, embodiments can be used to separate and bond entire devicestructures, including a fully-formed transistor layers and multi-levelmetal interconnect networks onto suitably chosen temporary separationlayers for later fabrication and device integration processing. This maybe followed by subsequent separation from the carrier substrate.

The methods and apparatuses according to embodiments can also be used toseparate and bond uniform, high-purity and crystalline layers to beformed into electrical, mechanical or optical devices followed bysubsequent separation from the carrier substrate.

FIG. 18 is a simplified view of the bonding a high-purity, singlecrystalline transfer layer onto a chemically or mechanically “weak”separation layer on a substrate. The upper crystalline transfer layer isformed to the desired thickness by the use of high-energy protonimplantation and room-temperature separation along the peak of theproton distribution. The upper transfer layer can be a uniformcrystalline layer or including a combination of IC, mechanical oroptical devices and their corresponding metal interconnect networks.

Embodiments may also provide proton implants useful for separation andlayer transfer stacking of highly-sensitive CMOS device structures. Aspreviously mentioned, embodiments utilize high-energy proton implants toform a Hydrogen-rich cleave surface several microns below the combinedthickness and stopping power effects of a combination of top layers ofphoto-resist or CVD dielectrics, and a multi-layer metal interconnectnetwork and transistor layers.

Radiation damage effects arising from the passage of a high-dose,high-energy proton beam through the metal interconnect and transistorlayers, may be at manageable levels—recoverable by standard annealingcycles at modest temperatures. Moreover, where specific radiation damageeffects are of particular concern, embodiments can include animplementation that bypasses concerns for radiation damage effects indevice dielectric layers.

One issue relating to possible radiation damage during high-dose,high-energy proton implants into CMOS device layers and their associatedmetal interconnect network layers, is bond-breaking effects in variousdielectric layers. This can be due to electronic stopping events fromthe passage of the energetic proton beam or from UV-radiation fromion-electron relaxation following recombination event in the acceleratorbeam line.

When the high-dose, high-energy proton implantation is performed atspecific points during the CMOS device fabrication process, radiationeffects from the proton beam can be substantially avoided. One point inthe CMOS process can be identified as occurring after the hightemperature (e.g., greater than 500° C.) processes associated withactivation of dopants in CMOS junctions are completed, and before thedeposition of sensitive gate stack oxides and subsequent incorporationof inter-layer dielectrics in the metal interconnect network.

At such a point in the CMOS fabrication process, the principal materialin the device wafer is crystalline silicon in doped junctions, withpoly-silicon filled lateral isolation regions, and the substrate wafer.The only substantial, long-term radiation damage effects inpredominantly silicon material are associated with lattice damagearising from the nuclear stopping components of the proton slowing downprocess.

Lattice damage events for a high-energy proton beam may be localizednear the peak of the proton profile. According to embodiments, that peakmay be placed several microns below the CMOS junctions in the transistorlayer and provide key hydrogen-trapping sites for localization of thecleave surface during layer separation. The several micron separationbetween the CMOS transistor layer and its associated carrier depletionlayers and the proton-induced lattice damage in the region of thesubsequent layer separation, may be sufficient to avoid risk fordeleterious device effects from the proton lattice damage layer.

In many advanced CMOS devices, the gate stack regions are initiallydefined by temporary films and structures which are “replaced”, aftercompletion of the high-temperature thermal cycles, by final devicestructures incorporating high-dielectric constant (“high-k”) gate oxidesand multi-layer metal gate electrodes. Following the “replacement gate”fabrication cycles, the material properties of the final gate andinter-metal layer (“low-k”) dielectrics limit allowable thermal cyclesfor the final CMOS device fabrication process to be less than 500° C.

A high-dose proton implant performed at the point just before the“replacement gate” fabrication, would avoid risk of damage to the finaldevice gate and inter-metal layer dielectrics and would not be exposedto 500° C. or higher thermal cycles, that could lead to spontaneouslayer separation prior to the desired non-thermal separation process atlayer separation after the fabrication of the transfer device layers iscompleted.

FIG. 19A shows a simplified cross-sectional view of high-energy, highdose proton implant to form a Hydrogen-rich layer placed several micronsbelow the CMOS transistor layer. This is performed after completionof >500° C. anneals associated with dopant activation in the transistorjunctions and before fabrication of “replacement gates” including finaldevice gate dielectrics and metal gate electrodes.

FIG. 19B is a simplified cross-sectional view of CMOS device layersafter completion of the formation of final gate stack and metalinterconnect structures, with a Hydrogen-rich layer formed by ahigh-energy, high-dose proton implant performed just prior to the“replacement gate” fabrication steps. The materials properties of thefinal gate and inter-metal layer dielectrics limit the fabricationprocess temperatures to be below 500° C., which also avoids conditionsleading to spontaneous splitting along the Hydrogen-rich region prior tothe desired separation, by non-thermal approaches, after completion ofthe full device structure.

Utilization of methods and apparatuses according to embodiments maypermit modulation of inter-layer bandwidth by stacking order andinter-layer thickness. Specifically, a principal goal of 3DIC stackingis to provide an alternative path for increasing the bandwidth forsignal processing communications between devices.

Bandwidth is the product of the data signal frequency, oftenapproximated by the CPU clock frequency, and the number of externalcommunication channels. For much of its history, IC development hasfocused on increasing the CPU and other data processing chip cyclefrequencies, possibly at the cost of increasing chip power use. Thenumber of communication channels has been limited by the density of bondpads available along the periphery of a planar device.

The development of 3DIC stacking methods has increased the possiblenumber of vertical channels, measured by the density inter-layercommunication lines. This density of inter-layer communication channelsincreases as vertical connection channel density increases. A convenientmeasure of the density of inter-layer connections is the inverse squareof the communication pin separation or “pitch”. Specifically, IOdensity=1/(pin pitch)².

The minimum metal channel or “pin” pitch, depends on a variety ofprocess and device considerations. One factor is the aspect ratio (AR)of the inter-layer metal channels: the ratio of the metal line diameterto the length of the via hole to be filled. Conventional “ThroughSilicon Via” (TSV) structures may typically exhibit an AR of betweenabout 5 to 20. This is significantly higher than the typical designrules for vias in high-density metallization for IC devices—often withan AR of less than 2.

One device consideration affecting the packing density of conventionalTSV structures, is the inter-device stress arising from the differentthermal expansion of micrometer-scale Cu cylinders and Si devicematerials. The undesirable local stress in the immediate surroundings ofa Cu via line can lead to design rules defining micrometer-scale “keepout” zones, where active circuit element are excluded from the vicinityof Cu via landing pads. This affects circuit density, performance, andyield.

Accordingly, methods and apparatus of specific embodiments may provideone or more procedures to locally increase the inter-level metal channeldensity and corresponding communication bandwidth between adjacentdevice layers. Use of high-energy, high-dose proton implants through asubstantially completed metal interconnect network and fully formed CMOStransistor layer for formation of a Hydrogen-rich region for non-thermallayer separation and bonding onto a 3DIC stack, provides an inter-layerseparation of a few micrometers (or less, for the cases of device layerson SOI buried oxides or other device types with minimal carrierdepletion layer thicknesses). This allows substantially less inter-layerseparation than the tens of micrometers typical of present day TSV andinterposer stacking methods. The thinner inter-device Si layers andelimination interposer and associated adhesive layers provide byembodiments allows for fabrication shorter and thinner inter-devicemetal signal connections and greatly reduces the “dead zone” effectsarising from thermal stress of present day several microns thick Cu TSVchannels.

Where high inter-layer bandwidth is desired (e.g., connections from CMOSimage sensor layers and signal processing devices), some embodiments mayemploy a variety of layer transfer techniques to align and bond the toplayer of the metal interconnect network of the transfer device tointer-layer connection channels in the top layer of the metal network ofthe lower device layer in the 3DIC stack. Such layer transfer approachesare outlined in FIGS. 12 through 15.

With this particular procedure, the inter-layer communication channeldensity can be expected to be similar to the pin density in the toplayer metallization layers in the two device layers, with pin pitch onthe order of a few micrometers or less. This “top-to-top” layer bondingresults in a factor of 100 to 1,000× higher inter-layer connectiondensity, and corresponding increased bandwidth, than existing 2.5D and3D chip stacking technologies.

FIG. 20 shows a simplified cross-sectional view of a “top-to-top” metallayer bonding of a transfer device layer and a lower device layer in a3DIC stack. This approach can provide inter-level metal connectionchannel densities, and corresponding increased bandwidth, similar to viadensities of the top metal layers of CMOS devices.

Specific examples of 3DIC structures according to embodiments may becharacterized by an IO density (in Pins/cm2) of between about 1.0E+06−1.0 E+08, over a pin pitch range (in nm) of 1.E+02−1.E+04. In anexample, for a TSV depth of 1 μm, aspect ratios (depth:minimum width ofdiameter) may range from between 10 to 1 over a range of TSV diametersfrom about 0.1 to 1 μm.

As mentioned above, proton implantation to form a 3DIC structureaccording to embodiments, may take place at energies of about 1 MeV,including energies of between about 300 keV-5 MeV, about 500 keV-3 MeV,about 700 keV-2 MeV, or about 800 keV-1 MeV. Incorporated by referenceherein for all purposes, is U.S. Patent Publ. No. 2008/0206962.

It is noted that implant properties of hydrogen ions at such higherenergy ranges may vary as between the 40 keV energies typical of layertransfer processes for SOI wafer manufacturing. A first orderdescription is the ratio of the “half-width” of the proton profilereflecting “straggling” (<ΔX>), to the depth of the “projected range”profile (<X>).

Comparison of such <ΔX>/<X>results in an example, is as follows:

-   -   proton implant energy 40 keV: <ΔX>/<X>=0.196≈0.2    -   proton implant energy 1 MeV: <ΔX>/<X>=0.048≈0.05        Thus, the 1 MeV proton profile is “sharper” than the 40 keV        profile.

3DIC structures are commonly stacked at the wafer level. Wafer-levelprocessing, especially when combined with the directness of the transfermethods for fully-metallized CMOS devices described herein, hassubstantial advantages for economic and efficient processing.

Wafer-level processing of bonded structures typically assumes that thesame size wafers are used, and the placement of dies on the joinedwafers are closely coordinated to result in vertical stacked 3DICstructures after separation into discrete systems. These conditions arecommonly met for large-area logic and memory devices fabricated on 200or 300 mm Si wafers in mass-production foundry processing.

Many desirable components for communication linkage, such as RF tuners,amplifiers and the like, are considerably smaller in die size thancm²-sized logic and memory devices. These smaller die sized devices maybe fabricated on diverse wafer sizes such as 100 and 150 mm, and may usenon-bulk silicon substrates such as Radio-Frequency Silicon on Insulator(RF-SOI), GaAs, etc.

There are many challenges associated with stacked structures withdiverse die sizes. Device alignment is important, and can be complicatedby the thickness variation inherent to backgrinding processes used tothin dies. Total Thickness Variation (TTV) for backgrinding processesare typically in the range of about 5%. Such variation can compound whenmultiple layers are stacked, making it difficult to performsemiconductor forming processes to facilitate interlayer connection. Asa result, stacked devices employ relatively large solder bumps andinterposer layers to connect devices in a vertical stack. In addition,many devices use bonding wires to connect multiple layers that aredisposed side-by-side in a package.

Embodiments of the present disclosure include devices and processes for3DIC structures that include heterogeneous die sizes. Dies that areformed by performing ion implantation through circuit structuresincluding dielectric and conductive materials to cleave base substratessimplify the thinning process, and have less variation than backgrindingprocesses. TTV values that can be obtained by ionic cleaving may be, forexample, less than 2%, less than 1.5%, and less than 1.0%. In addition,backgrinding applies a substantial amount of mechanical stress tosemiconductor devices, which may disrupt structures in the device,causing further alignment and performance issues.

FIG. 21 shows an embodiment of a process 2100 for forming a 3DICstructure with different die sizes. An advantage of process 2100 is thatit combines the economic advantages of wafer-level processing with theflexibility of incorporating layers of smaller area dies, which may befabricated on a diverse variety of substrate materials and wafer sizesinto composite 3DIC structures.

A base device structure is prepared at 2102. FIG. 22 illustrates anembodiment in which a base device structure 2202 is prepared usinghigh-energy hydrogen implantation, where the peak concentration of ahigh-dose hydrogen implant is located in the substrate region below ametallized layer which may be, for example, a CMOS or MEMS device layer.

Following cleaving along an approximate location of the hydrogenconcentration peak, residual damage along the cleave plane is removedand the transferred device layer is bonded to another wafer-scale devicelayer as shown in FIG. 23. In the embodiment shown in FIG. 23, the basedevice structure 2202 includes two wafer-level bonded semiconductorlayers, 2202A and 2202B, which are formed by implanting ions throughdielectric and conductive structures that are formed on semiconductorwafers. In some embodiments, the base device structure 2202 may be morethan two stacked semiconductor layers or a single stacked semiconductorlayer.

FIG. 23 illustrates wafer-level bonding in a device orientation wherethe bonding occurs along the metalized layers of the two layers, wherethe upper (second) device layer 2202B is face down compared to the lower(first) device layer 2202A, which is face up. Although only a singledevice of each of the first and second device layers are illustrated inFIG. 23, in an embodiment, cleaving and bonding operations are performedon a plurality of devices on a wafer.

Before the two device layers 2202A and 2202B are bonded together, thereis an opportunity for deposition and patterning of one or moreintermediate layers 2204, insulated by inter-metal dielectric materials,that can provide both vertical (device to device) and lateralconnections for signal, timing, poser and ground connections. Suchinter-device metal connection layers 2204 are analogous in function toredistribution layers (RDL) in modern 2.5 D multi-chip packagingschemes.

After bonding of the first device layer 2202A to second device layer2202B, with inclusion of the intermediate connection layer 2204,vertical vias 2206 are etched and filled with metal to provideconnections between the device layers and a top surface array of bondsignal pads.

An interconnect layer 2208 is formed on the exposed upper surface ofbase device structure 2202 in process 2104. The interconnect layer 2208may include appropriate bonding pads on the top layer of the base devicestructure 2202 for direct pick and place addition of various smaller diecomponents, as well as lateral wiring connections to interface betweenthe contact pads exposed by the base device structure 2202.

In an embodiment, the top metal layers of interconnection layer 2208include multi-level metal networks for lateral communication, power andground connections for a composite device, with the addition of bondingpad arrays designed for placement and bonding of face-down metalconnections with smaller, diverse die types.

As illustrated in FIG. 24, one or more die 2210 is placed on theinterconnect layer 2208 in process 2106. The one or more smaller die2210 may be placed using known pick and place techniques to alignterminals of the one or more smaller die 2210 with the bonding padsexposed on the upper surface of the interconnect layer 2208. Thelocation and metal-to-metal bonding of discrete die types on a compositewafer-level bonded structure 2202 can be accomplished by an automateddie pick, place and bond apparatus.

In some embodiments, smaller dies 2210 have different sizes andthicknesses from one another. The smaller dies 2210 may be aheterogenous set of devices that perform different functions, or ahomogenous set of devices.

Since dies 2210 may have various thicknesses, and in some embodimentsmay be thicker than the desired substrate thickness (e.g., in the rangeof 1 to 10 um), a layer of deposited material with a similar erosionrate under CMP processes as the substrate die of the added smallerdevices may be formed between and over the dies 2210 at 2108.

For example, as seen in FIG. 25, dielectric material 2212 may bedeposited over exposed surfaces of the device structure including dies2210 in process 2108. The dielectric material 2212 provides forelectrical isolation of the smaller dies 2210. The dielectric material2212 may be one or more of a variety of materials commonly used in thesemiconductor industry that provide insulation from stray current flows,including a CVD oxide or other suitable insulating material.

In some embodiments, a filler material 2214 is deposited over thedielectric material 2212 at 2110. When the dies 2210 are Si devices, thedeposited layer may be plasma deposited poly-Si or amorphous-Si. Thefiller material 2214 may be selected to have a similar erosion rate tothe dielectric material 2212 and the substrate material of the smallerdie devices 2210 when planarizing the structure at 2112, for example byperforming CMP.

Although process 2100 and the associated figures describe forming aseparate dielectric material 2212 and filler material 2214, in someembodiments only a single material or more than two materials aredeposited over the dies 2210.

A planarization process is performed at 2112 to planarize the uppersurface of the device until contact pads are exposed. The slurrychemistry for the CMP process may be selected based on the dielectricmaterial 2212 and the filler material 2214 to achieve approximatelyequal erosion rates of the substrates in the added smaller diestructures 2210 and the deposited over-layer materials. In anembodiment, planarization process 2112 thins the added smaller die 2210substrates to thicknesses of about 10 μm or less for later formation ofvertical metal vias for interconnection with later added structures andbonding pads. In an embodiment, planarization 2112 is performed until inan overall layer thickness of 10 to 30 μm is obtained.

In addition, planarization process 2112 provides a planar top surfacefor the newly enlarged composite device structure for subsequentaddition of multi-level metal interconnects for lateral signal, powerand ground connections as well as bonding pads designed for connectionsof additional layers added to the composite structure with wafer-levelor discrete die placement methods. In an embodiment, the planarizationprocess 2112 may be performed on the top surface until the surfaceroughness has an R_(A) value that is 5 Angstroms or less, or 3 Angstromsor less.

The deposition and planarization elements of process 2100 may beperformed such that substrates of the smaller dies 2110 are thinned to adesired thickness. In addition, the dielectric and filler materials 2208and 2210 provide mechanical support, and in some embodiments one or moreof the layers formed over dies 2110 facilitate heat transfer out of afinal 3DIC structure.

In some embodiments, no additional layers are placed on the smaller dies2210. In those embodiments, the device may be packaged afterplanarization 2112 without placing upper device structures on thesmaller dies 2210.

As illustrated in FIG. 26, interconnect structures 2216 to electricallycouple at least one of the one or more smaller dies 2210 to upper devicelayers 2218 of the 3DIC are formed at process. The interconnectstructures 2216 may be formed on exposed surfaces of smaller dies 2210,and/or on an exposed surface of upper device structure 2218 before it isplaced onto the smaller dies. In various embodiments, the upper devicestructure 2218 may be a single substrate as illustrated in FIG. 23, twowafer level bonded substrates, or more than two substrates.

Embodiments of process 2100 provide for the addition of layers ofdiscrete dies to a wafer-level process flow for bonding of multi-leveldevice structures into a composite 3DIC structure. A device madeaccording to process 2100 may have lateral electrical isolation ofdiverse added dies in the multi-chip layer, and may include verticalmetal connections in dense, high-band width networks as well as lateralmetal connection networks for the composite device structure containingwafer-level and discrete die placements. When smaller dies of differentthicknesses are provided, process 2100 can accommodate these structuresby planarization and thinning of the diverse substrates in the compositedevice layer.

In the course of 3DIC fabrication using wafer-level transfer ofmetalized transistor and MEMS device layers, situations arise where itis advantageous to locally adjust the depth of the hydrogenimplantation, which determines the approximate local location of thecleave plane in the in-process step for layer transfer.

A major challenge for operation of dense high-performance circuitelements with 3DIC stack arrays, such as micro-processor logic andgraphics processors for image analysis and display drivers, is theremoval of heat from active device cores.

As described above, a network of channels for flow of coolant fluids canbe formed in close proximity to a heat-generating transistor layer byadjusting the local penetration depth of the hydrogen implant profile byadding a patterned “range adjusting” layer comprised of materials formedat a sufficient thickness to result in a local offset in the hydrogendepth and subsequent cleave surface. After cleaving of the devicetransfer layer along the variable depth cleave surface, a network ofchannels can be formed in the bottom surface by bonding the transferdevice layer to a planar surface, such as the planarized top layer ofanother device layer, as shown in FIG. 1.

The range compensating layers may comprise patterned layers of CVDsilicon oxide of appropriate thickness combined with an unpatternedsilicon nitride layer, which acts as an etch stop for the removal of thepatterned oxide layer after the implant step. In another embodiment, therange compensating layer is a patterned layer of thick photoresist.

FIG. 27 shows an embodiment of a device that includes diverse sized dies2710 disposed between a lower which has several features that are notpresent in the device of FIG. 26. The diverse dies 2710 are formed overa base device structure 2702, which includes upper and lower parts thatmay be formed by implanting ions through metal and dielectric structuresto form a cleave layer at the wafer level, and bonding the upper andlower parts to form the lower device structure 2702. In addition, thedevice of FIG. 27 shows a plurality of cooling channels 2720 that aredisposed at the interface between the upper and lower parts of the basedevice structure 2702, and at a lower surface of the substrate of upperdevice structure 2718.

Another feature of the device shown in FIG. 27 that is different fromthe device of FIG. 26 is the location of vertical interconnectstructures. While the embodiment of FIG. 26 has vertical vias 2206 thatpenetrate the upper device structure 2218 and filler material 2214, FIG.27 shows vertical vias 2722 that pass through small die structures 2710to provide electrical communication between devices of the lowerstructure 2702, the small dies 2710, and the upper structure 2718.Persons of skill in the art will recognize that numerous variations arepossible beyond the specific features shown in FIG. 26 and FIG. 27.

Processes according to the present disclosure may be applied fortransferring devices which contain large variations in the density oftotal metal layers in local regions of the transferred device. Whenimplanting hydrogen ions through metal and dielectric structures of asemiconductor device, the depth of the cleave plane may be affected bythe arrangement of conductive and dielectric structures in a circuitlayer. For example, as seen in FIG. 28, the depth of peak energy, whichmanifests as a cleave plane, may be less in a high-density area of adevice than a low-density, or sparse area. In some circumstances, it maybe desirable, for purposes of process simplicity in the layer transferbonding, to have the implanted hydrogen profile depth at the same planarlocation below a circuit layer.

Hydrogen cleave plane depth can vary in between different areas of ahigh-performance microprocessor where a dense, multi-layer metallizationlayer over the logic core is surrounded by more sparse metalinterconnect networks in memory (e.g. embedded SRAMs) and timing andinput/output circuits. Other examples include optical sensor (cellphonecameras, etc.) devices where densely metalized image processing circuitsare surrounded with more sparsely metalized photosensor arrays. Inaddition, MEMS devices often contain multiple layers and open spaces ofvarious material densities. These variations can translate to differentstopping powers for hydrogen ions, which can vary the depth of a cleaveplane. In an embodiment that includes transferring devices containingMEMS devices.

As seen in FIG. 29, local hydrogen profile shifts can be compensated forby a patterned range compensating layer 2902 of appropriate thicknessand hydrogen stopping power to result in an approximately planarhydrogen peak profile depth and cleave plane. Accordingly, embodimentsof the present disclosure may include forming a range compensating layer2902 over a top surface of a semiconductor device to compensate forvariations in ion penetration depth resulting from variations in densityand/or the types of materials present between an upper surface of thesemiconductor device and a cleave plane.

In some embodiments such as the example illustrated in FIG. 29, thecompensating layer 2902 has an even thickness, and is selectivelydeposited over areas of the device which would otherwise have a higherion penetration depth than areas with no compensating layer. In otherembodiments, the compensating layer 2902 has variations in thickness toaccount for multiple variations in ion penetration depth. For example, ashape of the compensating layer 2902 can be developed by performing ionimplantation on a device that lacks a compensating layer, measuringdepth variation in the cleave plane, and forming a compensating layerwhose thickness varies as a mirror image of the depth variation, e.g.greater depth ion penetration areas would correlate with thickersections of the compensating layer, and vice versa.

Closely spaced stopping power variations over lateral scalesapproximately equal to the lateral straggling of high-energy hydrogenions, on the order of 1 or more microns, are not generally replicated invariations in hydrogen profile depth. Accordingly, the thickness of therange compensating layer 2902 may vary from one functional region of acircuit to another, as opposed to varying based on individual nano-scalestructures within a region.

In an embodiment, provisions are made for active removal of heatgenerated by circuit switching and resistive power losses in avolumetric 3D composite multidevice layer system by formation of coolingchannels formed along the cleave surface defined by a high-concentrationHydrogen profile. The cleave surface depth is defined by the thickness,stopping power and location of patterned layers added to the devicesurface before Hydrogen implantation.

As illustrated in FIG. 2A, embodiments of the present disclosure includea cooling channel. In the example of FIG. 2A, he cooling channel wascreated by modulating a depth profile of implanted Hydrogen with apatterned CVD oxide overlayer that is present when hydrogen is implantedto form a cleave layer. An associated CVD nitride layer is used toprovide an etch stop for the CVD oxide layer patterning. Both of the CVDnitride and oxide layers are removed in later processing.

FIG. 2 illustrates an embodiment of cooling channels formed along thecleave surface by offsetting the proton depth with a patterned stoppinglayer photoresist (PR) layer. In other embodiments, the stopping layermay be a similar dense material deposited on the device wafer surface.The thickness and stopping power of the underlying un-patterned PR layercan be used to modulate the depth of the cleave surface features in thesubstrate material below the transferred device layers. FIG. 2 shows theformation of a completed cooling fluid channel by bonding the modulatedcleave surface to a planar top surface of an underlying device orsubstrate layer.

In an embodiment, cooling channels are enhanced by applying a surfacecoating. A surface coating material may be selected to improve heattransfer from the active device layers to a cooling fluid in the coolingchannels, and/or to reduce or eliminate chemical reactions between aheat transfer fluid in the cooling channel and a substrate material. Forexample, in some embodiments, a cooling channel is disposed in a layerwith high thermal conductivity, and the high thermal conductivitymaterial reacts with a heat transfer fluid that flows through thecoolant channel. In such an embodiment, exposed surfaces of the coolantchannel may be coated with an inert material such as an oxide or nitridematerial that prevents chemical reactions between the heat transferfluid and the high thermal conductivity layer material. For example, theinert material may be SiO₂ or Si₃N₄.

Persons of skill in the art will recognize that characteristics of thecoating material including material type, thickness, and depositiontechnique may be selected based on the particular thermal conductivitylayer material and heat transfer fluid used in an embodiment. In someembodiments, the coating material assists in heat transfer, and has ahigher thermal conductivity than a substrate material over which thecoating is formed. Other favorable characteristics of a coating layer oncoolant channels include excellent adhesion to the coolant channel wallmaterial, uniform conformal coating thickness for good thermalconductivity and free flow of coolant materials and, being inert to thecoolant fluid material at device operating temperatures.

In an embodiment, a fluid in the coolant channels may be a heat transferfluid with a relatively high thermal conductivity. In some embodiments,the fluid is an inert substance such as water, or a highly dilutesolution. In other embodiments, the heat transfer fluid may be ananofluid that comprises nanoparticles that enhance the thermalconductivity of the fluid compared to the liquid phase component. Theheat transfer fluid may circulate through an external heat exchanger totransfer heat away from the device.

The location of the cooling channel can be chosen to be at a transferdevice bond layer as seen in FIG. 2, or in an alternate location forcases where direct bonding of device metal layers is desired, forhigh-bandwidth circuit connections, as seen in FIG. 20. In FIG. 20, thecooling channels are located near a planar bond surface for asubsequently added device layer.

In some embodiments, one or more heat transfer layer may be included ina 3DIC device. A heat transfer layer may be a material that has superiorheat transfer characteristics to materials used in an active layer. Theheat transfer layer may be disposed adjacent to the cooling channels, sothat a heat transfer fluid travelling through the cooling channelstransfers heat from device circuitry to the heat transfer layer. Inother embodiments, cooling channels are formed directly in a highthermal conductivity heat transfer layer.

Multi-layer lamination of devices allows for the insertion of layers ofhigh-thermal conductivity materials and interfaces to improve both thelateral spreading of heat from local active circuit regions and thevertical transfer of heat to the network of fluid flowing in coolingchannels. The provisions for controlling the local depth of the cleavesurface in materials also allows for the formation of cooling channelsin subsequently laminated high-thermal conductivity layers in a similarfashion as the transferred device layers. For example, FIG. 16illustrates a high thermal conductivity heat spreading layer withcoolant flow channels that is bonded between two circuit layers by CVDoxide bond layers.

As indicated in Table 1 above, the room-temperature thermal conductivityof Silicon, the dominant substrate material for current IC fabrication,has a relatively high thermal conductivity, matched closely only bySilicon Carbide (SiC). In an embodiment, it is desirable to use amaterial that has higher thermal conductivity than Si as a high thermalconductivity layer.

A consideration for a material for a high thermal conductivity heattransfer material is the thermal conductivity properties of materials attemperatures characteristic of active circuit operations, which aregenerally in the range of 80 to 120 C. For Si at room temperature (25 C,300K) and above, thermal conductivity decreases strongly with increasedtemperature, leading to a risk of “thermal runaway” for local regionsheated by active circuit power. As seen in FIGS. 30 and 31, Si thermalconductivity decreases at all temperatures for increased dopantconcentrations due to phonon-dopant scattering. For commonly used Sisubstrates, the dopant levels are relatively low (≈10¹⁵ dopants/cm³)leading to relatively high thermal conductivity compared to the higherconcentrations illustrated in FIGS. 30 and 31.

FIG. 32 illustrates thermal conductivity of 6H-SiC at varioustemperatures and doping concentrations as reported by Morelli et al.(1993). In the FIG. 32, sample 1 is a very pure or highly compensatedsample, and the remaining samples have electron concentrations asfollows: sample 2—n=3.5×10¹⁶ cm⁻³; sample 3—n=2.5×10¹⁶ cm⁻³; sample4—n=8.0×10¹⁷ cm⁻³; sample 5—n=2.0×10¹⁷ cm⁻³; and sample 6—n=3.0×10¹⁸cm⁻³. Thermal conductivity values of various forms of silicon carbideare reported as being higher than silicon, with conductivity values of3C, 4H and 6H polytypes being twice as high as silicon at 300K.

As illustrated in FIG. 33, thermal conductivity of some carbon-basedmaterials is much higher than silicon. In particular, diamond, graphite,graphene and Carbon nano-tubes all have thermal conductivity values thatare substantially higher than thermal conductivity of silicon,especially at higher temperatures. While FIGS. 30 and 31 show a steepdecline in silicon's thermal conductivity above room temperature, thedecline in thermal conductivity of carbon-based materials is relativelyshallow, and in the case of amorphous carbon, thermal conductivityincreases above room temperature. In particular, thermal conductivityvalues reported for diamond and graphene are an order of magnitudegreater than thermal conductivity of silicon at 300K. Another materialwith a high thermal conductivity that is comparable to forms of diamondis cubic Boron Arsenide. In embodiments of the present disclosure, oneof these materials may be used as a bulk substrate material.

In the present disclosure, the term “plane” is used to describe a cleaveplane, which is generally understood to be a location at which a cleavedlayer is separated from a substrate. However, as explained above, arange compensating layer may be applied to a substrate before ionimplantation, which can result in an as-cleaved surface that includesone or more contours which may define, for example, a cooling channel.Accordingly, use of the term “cleave plane” in the present disclosureshould not be construed as limiting embodiments of this disclosure tocleaved surfaces that are perfectly flat.

In an embodiment, a chemically or mechanically weak cleave surface isformed by ion implantation prior to the formation of any sensitive orreliability concerned device layers, interfaces of structures. Such anembodiment may be used in the formation of a full device structure,including a full network of metal interconnects and inter-metal layerdielectrics, to be followed by initiation of cleave action at thepre-formed cleave surface for transfer to a 3DIC stack structure.

Such an embodiment would reduce concerns for device yield andreliability problems related to the formation of the buried cleavesurface. In the case of Hydrogen-based cleave surface formation, thisembodiment allows for use of substantially lower proton ion energies forthe implant step for a desired cleave surface depth.

Benefits of such an embodiment include that the mechanical, thermal andchemical conditions for the post-cleave plane formation devicefabrication and testing process should be conducted to avoid prematureinitiation of the cleave action. In an embodiment that usesHydrogen-driven cleaving, this involves restricting the post-cleavesurface formation processing to temperatures below ≈500 C.

Many advanced devices, for example those which contain high-dielectricconstant, or high-K, gate oxides, such as HfO₂ and related forms, havethermal budget restrictions in this general area.

FIG. 34 illustrates a bonding step for a transfer layer. In anembodiment, the transfer layer is a high-purity, crystalline transferlayer that is bonded to a substrate layer containing a chemically ofmechanically weak separation layer that can subsequently be cleavedafter initiation of appropriate cleave surface formation conditions.

FIGS. 35 and 36 illustrate an embodiment of forming a buried Hydrogenprofile with peak concentration appropriate for formation of a cleavesurface at a depth below a partially completed device layer, prior toformation of sensitive device layers, interfaces or structures. FIG. 36illustrates a fully completed device structure, including fullyconstructed metal interconnect and inter-metal dielectric layers priorto introduction of process conditions for initiation of a cleave surfaceat the buried Hydrogen-rich cleave surface.

A process may be performed where a chemically or mechanically weak layeris formed in a partially completed device substrate prior to theformation of sensitive device layers, interface or structures. Thermal,mechanical and chemical processing of the subsequent device fabricationmay be restricted to conditions which do not initiate cleaving action atthe cleave surface locations. The sensitive structures may include gatedielectric and inter-metal layer dielectric layers. An example of asubsequent process restriction for the case of a Hydrogen implant formedcleave surfaces include processing at temperatures at or below 500 C. Inan embodiment, the completed, fully-metallized device structure istransferred to a 3DIC stack following cleaving initiated at the cleavesurface.

Control of implant conditions during proton implantation is importantfor successful layer transfer of electronic devices. One aspect of thiscontrol is the radiation damage associated with the passage of protonsthrough electronic device materials and into an underlying substrate.

As energetic ions enter solid targets they transfer kinetic energy inthe slowing down process through collisions with the target material.The details of this stopping process are important since the energytransfer from the passing protons generates several forms of materialdisruption, or damage, that play specific roles in the layer transferprocess and in the performance of the transferred electronic devices.

Despite the complexity of the possible collisions and otherinteractions, the stopping of ions is dominated by two major categoriesof collisions: (1) collisions between an energetic implanted atom andcore electrons and nuclei of the target atoms, referred to as nuclearstopping, and (2) collisions between the energetic atoms and looselybound electrons in the outer shell of target atoms, which is referred toas electronic stopping.

The effects caused by these two forms of ion-target atom collisionsdepend on the type of materials in the target. In embodiments of thepresent disclosure, the types of target materials include electronicdevices and surrounding structures. Nuclear stopping collisions resultin a large transfer of kinetic energy to the target atoms, oftenknocking the target atom out of its original lattice site and creatinginterstitial target atoms and vacant lattice sites. These interstitialsand vacancies can combine with similar defects to form stablestructures, which may be collectively referred to as implant damage.

In a layer transfer processes that uses proton implants there areeffects of residual implant damage. During and soon after performingimplantation, the accumulated recoil damage from the nuclear stopping ofprotons in the target leads to formation of stable damage structureswhich provide effective trap sites for the implanted protons. The protontrapping in the implant damage layer near the end of the ion tracksholds the Hydrogen in place, rather than quickly diffusing away, andallows for formation of Hydrogen-filled platelets which are the seedsfor the formation of cleave surfaces that allow for separation of atransfer device layer from a substrate.

Electronic stopping in electronic materials results in local scatteringof electrons, often referred to as “ionization.” In conductivematerials, such as Cu metal lines and doped Si materials, localscattering of electrons may be rapidly repaired by the local motion ofelectrons in these materials. However, in insulating materials, such aslow dielectric constant (low-k) layers that are used to insulate Cu andCo metal interconnect layers, high-dielectric (high-k) oxides commonlyused as gate dielectrics between the CMOS gate and channel regions andoxide or nitride spacers formed along the sidewalls of gate electrodes,local electron scattering cannot be easily neutralized, resulting inisolated charged regions and trap sites related to broken atomic bondsin the dielectric materials. The present application discloses processesthat repair such damage.

Key aspects of proton range and damage effects can be illustrated byMonte Carlo modeling, e.g. modeling conducted with Stopping and Range ofIons in Matter (SRIM) software. An example of SRIM modeling of protonrange and damage effects is illustrated in FIG. 37.

FIG. 37 is a graphical illustration of a model calculation for 1 MeVprotons implanted into a 3 μm thick multilayer containing Cu metal andSiO₂ dielectric layers on a Si substrate with a CMOS device layerlocated just below the metal/oxide multilayer. The proton tracks showthat 1 MeV protons extend deeper than 10 μm below the top metal layer.In addition, FIG. 37 shows that ions injected at a single point on thewafer surface spread laterally over several microns near the deepestportions of the profile, which is referred to as lateral straggling. Theproton insertion at a point on the metal/oxide multilayer surfaceresults in a spread of implanted protons approximately 15 μm below thesurface and several μm in lateral directions.

FIG. 38A illustrates 1 MeV proton and target atom recoil profiles forhigh-dose protons implanted through the 3 μm thick metal and oxidemultilayer structure, CMOS transistor region and silicon substrateillustrated in FIG. 37, while FIG. 38B illustrates the correspondingionization profile. In FIG. 38A, the depth profiles for the implantedprotons have a peak concentration at about 14 μm below the top surface,which is about 11 μm below the CMOS transistor and depletion layers.

Both the proton and Si recoil distributions are sharply peaked near thedeep portions of the implant profiles. The Si recoil concentration atthe CMOS device layers, which are about 3 μm deep, is more than tentimes lower than the recoil concentration peak at the approximate depthof the layer cleave surface, which is 14 μm. The high levels of Sirecoils at the depth of 14 μm depth produce, under proper processconditions, a dense network of accumulated damage structures that serveto trap the implanted Hydrogen in place.

Another effect of proton passage through the model device layers is thedeposited energy from scattering of energetic protons by loosely boundtarget electrons. The deposited energy, typically referred to asionization energy expressed in eV/Angstrom, has strong peaks in the Cumetal and deep Si layers as seen in FIG. 38B. These effects are quicklyneutralized by motion of nearby electrons in these two conductivematerials. Although the deposited energy from electron scattering in theoxide layers is relatively small at about 4 eV/Angstrom in this example,any scattering collisions that results in a displaced electron creates abroken bond that is not readily repaired by electron motion in theinsulating dielectric layers.

While such damage may not have a strong effect on highly conductivematerials, it can have substantial deleterious effects on otherstructures, such as dielectric structures. The deleterious effects maybe less noticeable in certain relatively large-scale structures such asthin film transistors (TFTs) and some MOSFETS for which reducedswitching times and leakage currents are less important. However, theinventors of the present disclosure have discovered that the damagecaused by ion implantation through sensitive structures has a profoundeffect on smaller scale and high-performance devices such as modernprocessors and memory devices, to the extent that many high-performancedevices are rendered inoperable by ion implantation.

One way to reduce damaging effects of ion implantation is choosing anappropriate implantation energy. In an embodiment, the proton energy maybe set high enough so that peaks of proton and recoil damagedistributions are deeper than the location of the electronic devicetransistor layer and the thickness of a depletion layer formed when thedevice is at operating potential, e.g. 1 μm in 10 Ohm-cm Si, which is acommonly used resistivity. Any overlap of the proton damage layer withthe device depletion region could result in strong leakage currents,carrier recombination and other deleterious effects on the deviceperformance.

Since the cleave surface may be subsequently bonded to another surfaceto form a 3D stacked structure, the proton depth below the transistorlayer and the associated depletion width should allow for removal ofmost or all of the cleave surface damage region to form a bond surfaceof adequate planarity and smoothness for high-strength atomic bonding.

In embodiments, the implant conditions is set to be favorable for theformation a dense and stable accumulated damage region at the locationof the desired cleave surface with trapping of a significant portion ofthe peak proton distribution. In particular, embodiments may use highproton ion density beams, slow beam and wafer scan speeds, andmaintenance of the target temperature during implantation below theonset on in-situ annealing of recoil damage, which is approximately 100C for Si and lower for other materials of interest such as III-Vcompounds. Implant machines that are appropriate for embodiments of thepresent application include refurbished ion implantation machines thatwere produced before about 2002.

Thermal processing after implant and before cleaving along the Hydrogenrich layer, such as deposition of CVD layers, thermal treatment ofintermediate bond layers, etc. may be performed in order to maintain theintegrity of the Hydrogen trapping damage layers. Studies of Hydrogenrelease from implanted Si and examination of proton damage structuresafter thermal annealing suggest that a maximum allowed temperature tomaintain stable proton trapping is approximately 400 C. Accordingly,embodiments of the present application may include limiting all thermalprocesses performed after Hydrogen implantation and prior to cleaving totemperatures that do not exceed a maximum temperature that may be, forexample, 500 C, 450 C or 400 C.

The inventors of the present disclosure have discovered that damagecaused by Hydrogen implantations, including stopping and recoil damage,can be repaired under specific conditions. Without a repair operation,devices may have compromised performance or be completely inoperable.Recovery of damage associated with electronic stopping in diverse layersof electronic devices is important for success in 3DIC device stackingusing proton implant process techniques.

In an embodiment, a thermal process that repairs damage to thedielectric and conductive structures is performed at a temperature of350 C or greater in an environment that includes hydrogen gas.Conditions in a repair process should be sufficient to allow hydrogen topenetrate the device surface and bond to a molecule that was damaged byan implantation process. In one specific embodiment, the repairannealing is conducted at a temperature of 400 C in an atmosphere thatincludes from 2 to 5 percent hydrogen, with a remainder being one ormore inert gas.

In an embodiment, the repair annealing is conducted for a period of timethat is sufficient to allow the hydrogen gas to diffuse though circuitstructures in a device, which may include an interconnect network ofmetal and low-dielectric constant dielectric material, and to occupypassivating sites at damaged dielectric bonds. For example, in aspecific embodiment, annealing is conducted at a temperature of 400 Cfor one hour to repair implantation damage.

Several variables influence the appropriate time and temperature forimplant repair. The specific temperature relates to the amount of timeit takes Hydrogen to diffuse through metal and dielectric interconnectnetworks and gate stack structures to regions where damaged bonds arelocated, which may be specific to each device. The diffusion of atoms inmaterials is proportional to (Dt)^(1/2), where D is a diffusion rateexponentially dependent on temperature and t is the diffusion time.

For many silicon-based dielectrics and device designs, 400 C for onehour using a 4% Hydrogen and 96% Nitrogen gas blend is appropriate torepair implantation damage. A repair process may be performed at atemperature as low as 300 C. In another embodiment, a temperature of upto 500 C may be used. However, certain materials are sensitive toelevated temperatures. Exposing a device to elevated temperatures andlonger times may cause unfavorable phase changes in high-k dielectricgate oxides such as HfO₂, HfSiO₂, etc., loss of lateral dimensioncontrol on dopant diffusion in sub-20 nm gate length finFETs, anddegradation of dopant activation in laser-doped junction contactregions. With these principles in mind, persons of skill in the art willrecognize that appropriate thermal repair processes may be performed attemperatures from 300 C to 500 C and times of at least 30 minutes in agas environment comprising at least 1% Hydrogen.

Accordingly, persons of skill in the art will recognize that variationsin time, temperature and Hydrogen concentration may differ in variousembodiments as these variables are interrelated. A combination of lowertimes, temperatures and concentrations may not be sufficient to repairimplantation damage, while longer times and temperatures may cause theHydrogen ions accumulated in a cleave layer to diffuse into thesubstrate, or have other negative effects associated with an extendedthermal profile. Higher concentrations of Hydrogen are an explosivehazard. It is also possible to vary temperatures in a repair process.

Some embodiments may use a forming gas for a thermal repair processafter ion implantation. Forming gasses are a mixture of Nitrogen andHydrogen gasses with a Hydrogen concentration that is typically between3% and 5%. However, other embodiments may use inert gasses other thanNitrogen gas, and different concentrations of Hydrogen. For example,embodiments may use an inert gas such as Argon, and embodiments may useHydrogen concentrations of more than 1%. Lower concentrations ofHydrogen may require longer exposure times, while higher concentrationsof Hydrogen represent an explosive hazard. When performing the thermalrepair process, the Hydrogen gas penetrates exposed surfaces of adamaged device, and may terminate broken bonds in order to repairdamage.

Thermal anneals with forming gas or other hydrogen-bearing gas haveappropriate time and temperature conditions to allow diffusion ofHydrogen into the sensitive dielectric layers of electronic devices,including low-k insulators in the metal interconnect network, gateoxides such as SiO₂, SiON, high-k dielectrics such as HfO₂, and oxideand nitride spacer gate sidewall insulators. Materials with higher Kvalues are more sensitive to damage from implantation, so a thermalrepair process is increasingly effective for higher K materials. Forexample, a thermal repair process may be performed after implantingthrough materials having a K value of 10 or more, or materials having aK value of 15, 20, 25 or more. Specific high-K materials that benefitfrom a thermal repair process include hafnium oxide (HfO₂), hafniumsilicon oxide (HfSiO₂), hafnium silicate (HfSiO₄), tantalum oxide(TaO₅), tungsten oxide (WO₃), cerium oxide (CeO₂), titanium oxide(TiO₂), yttrium oxide (Y2O₃), strontium titanate (SrTiO₃), lanthanumaluminate (LaAlO₃), niobium pentoxide (NiO₅), zirconium silicate(ZrSiO₄), zirconium oxide (ZrO₂), barium titanate (BaTiO₃) and leadtitanate (PbTiO₃). Experimentation has determined that when ions areimplanted through high-K materials to form a cleave layer, circuits thatdepend on the high-K properties are not functional without performing athermal repair process according to an embodiment of the presentdisclosure.

In an embodiment, a thermal cycle for a repair process does not exceed athreshold for dissolution of the Hydrogen trapping implant damagestructure in the region of the intended cleave surface. If thetemperature exceeds the dissolution threshold, the trapped Hydrogen willdisperse into the substrate so that it is not possible to perform acleaving operation. In addition, the temperatures to which a substrateis exposed to after a thermal repair process may be limited to beingbelow a threshold value, e.g. 500 C, 450 C or 400 C after repairing andbefore cleaving to limit dispersion.

It is desirable to perform a thermal repair process to repair ion damagewith direct access for the ambient gas to the dielectric layers in themetal interconnect network and transistor gate stack regions. Thus, athermal repair process is performed prior to sealing of the electronicdevice surfaces. Accordingly, it is preferred to perform a thermalrepair process prior to performing deposition processes that could limitaccess to damage sites. In a 3DIC device, the thermal anneal isperformed before the layers are bonded.

In embodiments of the present disclosure, a network of channels for flowof cooling fluids is defined by modulation of implanted Hydrogen depthby a patterned layer of materials at the device wafer surface duringHydrogen implant with thickness, stopping power and location chosen tocreate a non-planar cleave surface in the transfer device substrate.Similar methods for modulating the depth of the cleave plane may be usedto define cooling channels in a selected high-thermal conductivitymaterial layer for subsequent insertion into a laminated multi-layer,multi-device 3DIC stack. In an embodiment, the surface regions of acooling fluid flow network are coated with material chosen to increasethermal conductivity between the heated device layer and substrate andthe flowing cooling fluid, and to prevent chemical reactions between thedevice substrate and cooling fluids.

Embodiments incorporate the advantages of wafer-level bonding processes,including incorporation of cooling fluid network channels, with a designflexibility for incorporation of dies fabricated on different wafersizes, different wafer thickness and different substrate materials.Devices formed using the cleaving and stacking techniques provided inthis disclosure have numerous advantages over conventional technologies.Substrates that are formed by backgrinding are subject to substantiallyhigher levels of mechanical stress and higher levels of thicknessvariation over the substrate surface. Ionic cleaving can be performedwith fewer process steps than backgrinding, simplifying the process andreducing the amount of handling required. Layers of the 3DIC structuresaccording to the present disclosure may be interconnected through densehigh bandwidth vertical and lateral metal connections, which maydisplace the need for interposer and solder bump structures, leading tosmaller, more tightly integrated, higher speed devices that are moreefficient to manufacture.

While the above is a full description of specific embodiments, variousmodifications, alternative constructions and equivalents may be used.Therefore, the above description and illustrations should not be takenas limiting the scope of the present disclosure.

1. A method for forming a three-dimensional integrated circuit (3DIC),the method comprising: providing a first substrate with a circuit layerthat includes plurality of dielectric and conductive structures;implanting ions through the circuit layer and into the first substrateto form a cleave plane; after implanting the ions through the circuitlayer, exposing the first substrate to a hydrogen gas mixture for afirst time at a first temperature to repair damage caused by theimplanted ions; separating a first portion of the first substrate withthe plurality of dielectric and conductive structures disposed thereonfrom a second portion of the first substrate by cleaving at the cleaveplane; and bonding the first portion of the substrate to a secondsubstrate.
 2. The method of claim 1, further comprising: connecting atleast a portion of the conductive structures of the first substrate toconductive structures of the second substrate.
 3. The method of claim 2,wherein the first and second substrates are wafer scale substrates. 4.The method of claim 1, wherein the first substrate is not exposed to anytemperature above 450 C after implanting the ions and before separatingthe first portion from the second portion.
 5. The method of claim 1,wherein the hydrogen gas mixture has at least 1% hydrogen gas and aremainder of the gas mixture is one or more inert gas.
 6. The method ofclaim 5, wherein the first temperature is from 300 C to 500 C.
 7. Themethod of claim 6, wherein the first time is at least 30 minutes.
 8. Themethod of claim 1, wherein the conductive and dielectric structuresinclude high-K dielectric structures comprising at least one materialwith a K of 10 or greater.
 9. The method of claim 1, wherein the ionsare implanted at a temperature of less than 100 C and a proton energythat is sufficient to place a majority of recoil damage and the cleaveplane deeper than a depletion layer thickness of an operatingtransistor.
 10. A method for repairing damage caused by implanting ionsthrough a circuit layer that includes conductive and dielectricstructures into a semiconductor substrate, the method comprising: afterimplanting ions through the conductive and dielectric structures of thesemiconductor substrate, exposing the semiconductor substrate to ahydrogen gas mixture for a first time at a first temperature.
 11. Themethod of claim 10, wherein the dielectric structures include high-Kdielectric structures.
 12. The method of claim 11, wherein the high-Kdielectric structures include at least one of hafnium oxide (HfO₂),hafnium silicon oxide (HfSiO₂), hafnium silicate (HfSiO₄), tantalumoxide (TaO₅), tungsten oxide (WO₃), cerium oxide (CeO₂), titanium oxide(TiO₂), yttrium oxide (Y2O₃), strontium titanate (SrTiO₃), lanthanumaluminate (LaAlO₃), niobium pentoxide (NiO₅), zirconium silicate(ZrSiO₄) and zirconium oxide (ZrO₂).
 13. The method of claim 10, whereinthe hydrogen gas mixture has at least 1% hydrogen gas and a remainder ofthe gas mixture is one or more inert gas.
 14. The method of claim 13,wherein the hydrogen gas mixture is a forming gas.
 15. The method ofclaim 10, wherein the first time is at least one-half hour.
 16. Themethod of claim 15, wherein the first temperature is from 300 C to 500C.
 17. The method of claim 10, wherein the first temperature is from 350C to 450 C.
 18. The method of claim 10, wherein the first time is fromone half hour to five hours and the first temperature is from 350 C to450 C.
 19. The method of claim 10, wherein the dielectric structuresinclude at least one dielectric material with a K of 20 or more, thefirst temperature is from 300 C to 500 C, the hydrogen gas mixtureincludes at least 1% hydrogen, and the temperature is at least 30minutes.
 20. The method of claim 10, wherein the implanted ions form acleave plane below the circuit layer.